I'd be inclined to include a "kill fee" of say 25% of the value if the buyer declines. 10% if you're feeling generous. Stores do it all the time; it's called a restocking fee. If it were of already existing work printed at your predetermined size, then they could return the work at no cost. I'd also include a clause in the sales contract/invoice that makes it clear work must be returned in identical condition to when it was delivered.