I used to have a restocking fee to cover the wasted free postage component incurred as sending an item that didn't eventuate a sale. 

Now i just absorb it as PR and keep it simple. As someone else posted, any hurdle in the way just causes buyers to either not buy in the first place or go the not as described route for trivial issues, which ultimately costs more.

Reality is returns are such a small % of sales that less time spent on them the better. The worry can exceed the actual impact.