eBay offers a Money Back Guarantee of 30 days after delivery for items that are not as described in the listing. If you’ve already burned through that but you paid for the battery with a credit card, you may be able to dispute the charge with your card issuer. The time limit varies by financial institution but is generally considered to be 180 days from the date of purchase.
Having said that, I’d never consider using an aftermarket battery in my iPhone pretty much for the reason you describe: lack of quality control and the risk of farking up my entire phone. This seller has 4.9% negative feedback over the past year for mostly battery purchases and that's considered a pretty high percentage, to boot. I consider the money I pay the service department at the Western Canadian mega-drugstore chain that’s also an authorized Apple service dealer to be money well spent.
composed and posted with an iPhone