Note: I made a few changes to this universe with my storyline.
Rule #1: Once you swap heads with someone, you can't swap back again for a month (30 days)
Rule #2: It's the law they have to swap back with you after that month is over if you request it. If they don't give it back, they are in violation of the law and can go to jail for body theft.
Rule #3: Legal contracts are binding to swap heads onto new bodies for a stated period of time. There are special lawyers for this.
Rule #4: No one under the age of 7 is allowed to swap with anyone. It's illegal for the 6 and under crowd.
It is generally assumed that the better the body someone has recently gotten, it's most likely a financial transaction. Some people swap for fun and have special groups where they can get together and swap for free, but for the most part it is a business transaction for those wanting a financial edge as they are starting out.
I'm keeping the bit about physical transformation: AFTER THREE MONTHS most people's head fully resemble the original head that the body carried around with it. There is a slow transformation that occurs after a few weeks. A full body/head swap is uncommon outside of financial transactions.
***
Mark and Ted went out for some beers at the local alehouse. Mark was ravenous. Ted ordered some hot wings but they weren't enough for Mark. Ted filled up quickly and watched with glee as Mark ate fish and chips, downed 2 more full glasses of ale and even drooled over a piece of chocolate cake for dessert. Mark didn't know what was wrong with him, because he never craved food like this before. But it was a direct result of the body he now possessed. It was addicted to greasy, fried foods, snacks and sugar. Ted, on the other hand, just had a small chicken salad and a handful of fruit salad. After dinner, Ted drove Mark home and handed him a garbage bag which included enough street clothes to last him a few days. Both of them were wearing each other's bodies but had kept their heads, and they were wearing each other's office clothes as well. Mark realized Ted had more expensive clothing than his own.
"Just so you know, those are my only dress clothes. I forgot to say," Mark said, somewhat apologetically.
"Don't worry, kid. We'll give you a uniform for the floor this weekend. As for me, I am going shopping soon for this new body. It's so exciting. My husband is going to flip out. I can't believe what an adjustment it is just to be five inches taller. It's such a rush. Thanks again for doing this!"
"Yeah. I guess now I just have to break it to my parents."
"Aw, they'll understand. You're making an investment in your future. Here's your copy of the contract. You'll get your money tomorrow. And uh, you're gonna need some of these. Trust me," Ted said, handing Mark a box of cigars. "We can raid my humidor later but that should last you for the time being." Mark's eyes went wide and he smiled and appreciative grin. He opened the box and took out a cigar and smelled it. The teenage boy had such a young looking face. Ted wondered how it would look in a month after it started to age up to look more like the old head.
"Cool. Is that why it feels all warm and stuff inside my chest?"
"Yeah. Hope your folks won't mind. You're gonna look like a stud, though. Welcome to adulthood!"
"My parents are so anti-smoking. I've always wanted to try one, though." Mark said, stuffing the cigars in his backpack and lumbered out of the car. He waved goodbye to his new boss, who drove off down the street. It was night now and the streetlights were on. Walking to the front door was a new experience. He felt like he was wearing a bunch of sandbags all over. 270 pounds! He had gained a hundred pounds. And he was itchy and hairy.
As he entered the house, he heard his parents in the kitchen talking.
"Hey. Guys? I've got something to tell you." Mark lumbered into the living room just as his mother distractedly walked in and gaped.
"What the HELL have you done? Whose body is that!" she shouted. Dad came in next. Mark's dad was a very handsome man with dark curly hair and thick stubble. He had a healthy, fit frame. An ectomorph, just like all the other men in the family.
"Did you trade with another fat kid at school? That body looks terrible! Why would you-?" His dad was flabbergasted.
"I know. I went to this job interview and the boss there made a deal with me. I traded bodies with him for a year."
"OH, Mark! I've warned you about this sort of thing!" His Dad chewed him out. "It's one thing to swap with family or friends to experiment. You should NEVER swap with a stranger at your age!"
"How much did he give you?" his mother asked impatiently.
"30K"
"30K? He took you for 30K? A swap like that is worth 60K easily!"
"He said 50...but, I'm going to get a promotion after a few months." Mark explained to them the plan for him to get a sweet deal making $28 an hour as a warehouse manager.
"That sounds fishy to me," his mother replied.
"28 an hour? Really?"
"Yeah, he says he's the owner and it's all perfectly legal. He'll teach me about management. I get promoted as soon as high school is over and it will be great for my resume."
"Well I guess there's nothing we can do about it now. Hope you enjoy being a middle aged man for the next year!" his mother said, throwing up her hands.
"Well, maybe it will be good for him. You can see how it feels to be older. You know you're going to grow into those looks pretty quickly. Was the guy bald?"
"Balding. Maybe by half his head."
"You can expect to lose all that hair within the first few weeks. It's one of the first things to go, you know."
"Looks like I'm gonna have to put you on a diet as well," Mom concluded. "You have to drop some of that. It's not good to drag around. You're 17 for crying out loud! Have you thought about how this will affect your social life?"
"I barely have a social life. I sacrificed it so I could be top of my class."
"What about swim team?"
"Oh. I hadn't thought about it," Mark said sheepishly. "I...guess they won't want to use me now."
"You're right. You look like you could do well with bowling, though, huh?" his dad said, trying to make him laugh.
Mark grimaced. He didn't like the idea of losing his hair in front of everyone at school all that much. He had rushed into this decision, for sure. Mark suddenly realized that he had to pee very badly. He went into the bathroom and discovered his new dick was about as big as his old one, so no massive change there. It was probably a half inch smaller than his usual 5.5 inches. So he had a 5 inch cock. He could live with that. He rubbed his big belly. He could barely see his cock under the folds of his new gut! He had hair just everywhere. He took off his new dress clothes and examined himself. He really did look like a freak show. 17 but with much younger looks. He looked like he was 13 or 14 at best, with a bloated pig cum-dumpster body. He started thinking about all the cocks that could fill his ass. He fondled his smaller dick and thought about it...before snapping out of it.
"Oh, gross." He fumbled with a meaty arm to find a shaver. He had so much body hair right now. Did he really want to make his new moobs even more visible? He pouted, then decided to leave himself hairy for the time being. Going to bed was another challenge. He had to lower himself more carefully. He played with his gut, making it ripple and ripple.
The next day, Mark put on some of his new clothes. His jeans were now a 45 inch waist size! He was technically obese now. He put on his new XXL polo shirt and grimaced. Even his shoes didn't fit anymore. Luckily, Ted had included a pair of size 12s for him instead of his usual size 10.
When he lumbered downstairs (which was much more difficult to do now) his mother refused him the regular sugar cereal he had loved for years.
"No. Here. I made you some oatmeal. You are not to eat ANY junk food at school, do you hear me?"
"Yes, mom." He ate glumly. He rubbed his tummy. He was still so hungry! He also had a burning sensation in his lungs and chest. He needed a cigar and he'd never even smoked one before!
"Hey, champ. Look, I think it would be a good idea for you and I to go to the gym together today. And every day. I know you usually work out at school but...I think it would just be better this way. We can't really afford a trailer. My gym is bare bones. No fancy stuff. Just the weights. But I know a lot about training."
Mark looked at his fit father. He had been fit enough but his father now shamed him. His father's body was muscular for an ectomorph. Mark's body had been skinnier and taut. Now it was just a giant BLOB. He shook his head, slightly embarrassed.
"Sounds good, Dad."
He suddenly thought with horror that he didn't want to go to school like this, but he had no choice.