Very simple answer. When you create a listing (or when the buyer has a look at the listing before buying) there is a clear option / information section that outlines returns. This section gives the seller the option regarding return shipping - either it can be paid by the buyer or seller. The default setting is "Return postage paid by: Buyer." For change-of-mind, that's all you need to know. It's very clear for the buyer to see before they choose to bid or buy.

Having said that, if the item is not as described or otherwise faulty, it's accepted that for good practice the seller forgoes the choice they made in the return policy and pays the shipping themselves.