What's the worst that could happen if....?
What's the worst that could happen if I sell a book that I do not 100% own on ebay.com or lulu.com or amazon.com
What if I like take a story, then like change 60% of it and publish it as my own and then the real owner report about me or the website finds out.
What's the worst that could happen to me ?
I don't live in the USA btw.
Since I have no idea where you live it would depend on how strict law enforcement and your judicial system is in your country. At the very least you could be sued for plagiarism. The website you attempted to sell on will turn over all information to law enforcement when they ask for it. It's also possible your accounts will be closed. It's possible for your court system to award the person a considerable amount of money, give you heavy fines, forbid you to have internet access for a number of years, have you arrested which will give you a police record, and an assortment of other nasty things.
You did say 'worst'.