Posted By:
PCNot sure why you're playing patty-cake with the seller -- you should get the full $100 as a refund. Period.
Open a PayPal dispute (I think you have 45 days from the date of purchase to do so), and then you have another 20 days to elevate it to a "claim", after which PayPal will refund your money in full if the seller cannot prove he sent the package or that you received it. Note that you can open the dispute and elevate it to a claim a second later (you do not have to wait).
I would also recommend sending the seller an email telling him you are going to initiate the refund process with PayPal, that he can make things easy by just reversing the full $100 payment (because he is going to lose under the PayPal process) and that you will not leave him a negative on eBay unless he leaves you one first.