Based on the eBay feedback they've been given, it sounds like they refund shipping both ways and the full price of the item. Given the fact that most online retailers have this policy for broken or defective items, I'd kind of expect this dealer to do the same. It seemed to be packaged pretty well so I doubt the clip could've broken off in shipping. It's certainly possible, but not very likely given the Eheim was packaged inside a box with bubble wrap, and that box was inside another with more bubble wrap.
I kind understand BryceM's position though. Being a college student and selling some of my old stuff, I think I'd die a thousand deaths if someone said something I thought was working really wasn't when it was received. I sell old stuff to try to make some extra money, not take a net loss on shipping. It does seem like he's trying to resolve the issue and it doesn't seem like there's anything malicious going on. In my opinion, as a business, I think the correct gesture would be to refund shipping both ways. I said I wasn't beyond giving positive feedback in an email so hopefully they'll look at that.
But honestly, in the grand scheme of things a $10 loss on shipping wouldn't be enough to go burning bridges and not recommending the seller. I'd probably just be happy to know the entire thing wasn't some elaborate scam and that I'll be getting a new, 100% working filter from Big Al's.

Plus, in my return to the hobby and fixing up of a 29 gallon and setup of a 20L shrimp farm...I think I'm pushing the $600 mark now. I'm just going to pay the credit card...and...not...look....