Whatever the rules, someone always, always tries to get around them. Its part of our DNA.
The challenge in setting up rules is balancing the accessibility of the majority that is willing to play along, while still making it difficult enough to prevent the determined from gaining too much unfairly.
A return policy that is too generous will result in returns of used junk, but returns that are too strict will breed more bad will than the "savings" can probably justify.
But you have to draw the line somewhere. I will always be too generous, too lenient, knowing that cracking down won't chase away the determined, but it may chase away the high-value customer.