This sounds like the perfect arrangement. They are easy to kill if you don't have the time and attention for them. Let someone else do the babysitting and enjoy your free tomato plants. I'm sure he'll sell the extras to account for his time and trouble.
I buy tomato seeds for a friend and for my work. They start the plants for me since I'm terrible at it and haven't ever been successful. I so admire the people who can grow strong tomato plants. My friend has a greenhouse and the one at work is climate controlled. I don't mind doing the shopping if they'll do the growing. Actually they were surprised that I offered to source the seeds they couldn't find in stores. I love to shop online so it was a way to repay their kindness.
I moved to the country a few years ago and these old timers around me are all about trading produce and services. I love it!