I've been using eBay for 20 years now and I don't think I've ever had someone not mail me what I ordered. I can't recall it every happening. Maybe I'm just lucky? It's not like I don't use it, I have a 1600 feedback rating at this point...
I buy from a lot of Chinese or Chinese resellers in the US. The Chinese based sellers I find are super reliable. The Chinese US based resellers, outlets, or whatever, used to be reliable, but it’s them I’m having issues with now. One cancelled my order outright and recently, one sent a tracking via DHL that basically showed nothing traceable and even EBay was perplexed. That one I got a refund. Then something similar happened with another... then another never even sent tracking information or anything. They don’t even respond to eBay once I open a case and contact them. It’s weird.