I used to work at Scotty's in New Smyrna Beach about 10 years ago or so while I was in college at UCF -- at the return desk of all things. We took Plywood back if it was in good condition (Ie no holes drilled in it, not warped, etc) and that was the only case. We did have people try to return things that were used like that, and basically politely turned them away on it and suggested to save it for the next storm.

Also, don't bother with 1/4" plywood, 1/2" or greater is the only thing that'll really do much. And during some cases people were buying hardwood plywood (which is massively expensive) to use for boarding up. It works, but it's a big waste in my opinion.