Make sure you understand the difference between
RESELL RIGHTS AND REPRINT RIGHTS.
If you only give away reprint rights that means the person can re-sell the book to anyone but cannot transfer the rights to resell the product to them. Resell rights means they can resell the book and they can give the resell rights to everyone who purchases the book.
Two big differences there, make sure you understand them. Not all books come with resell rights, some are reprint rights only.