The easilest solution to this is to decide on the value of partial refund that would be acceptable.

That needs to be the difference in value of the 2 items... But you also need to consider the cost of return postage.

So, if the difference was $100 - then just ask for part refund, and keep the item. You are then in front by the value of the return postage. And remember - the seller ALSO loses if you return the item, because they must refund the original postage.

So if you take it a Paypal Claim, the seller loses on the postage one way, and the buyer loses the postage on the return. That means it's a Lose <> Lose.

The seller should usually accept a reasonable partial refund request. Don't be greedy, make it a price that's worth it for both of you.

EG in the dispute white something like this (not perfect, just an idea...

The item that I received is worth $100 less to me than the item that I ordered. To comply with Paypal requirements, return shipping will cost me $80. If I return the item, the seller will lose the original postage costs, which are about $50.

To save myself $80 and the seller $50, I propose a partial refund of $150 would be fair. This will not leave the seller in a worse position than if I return the item for a full refund. The savings that I make from n ot having to pay for the return will subsidise my time and costs to resell the incorrectly supplied item.

If you word it cleverly, the situation can be made so that you don't lose. But if you stick to your guns, you will certainly lose the cost of return postage... and that will be heaps.

ONLY once this deal is agreed upon, then escalatate the dispute. If you escalate without the partial refund, then Paypal will force you to return the item. Also, make sure that you know and quote and explain the cost of return postage BEFORE you escalate. Your objective to to have Paypal read that you are being reasonable, and to recommend to the seller that what you are offering is a good thing for them to accept.

Sorry if I have made this explanation messy, it's hard to explain.