Customers using inaccurate return reason

How do you handle customers using "defective doesn't work" when they add a comment on the return that they just bought the wrong size? Is there any way to get the return shipping costs, as we have set up for these orders where a customer used an inaccurate return reason to avoid the shipping cost? I saw that safe-t claims are an option, but every time I have tried to use that system it says it is ineligible. We charge return shipping, period.