Might be more helpful if you state what kind of microsd card you are using, which version of retropie you installed, and which model of a Raspberry Pi that you own. And which software you are using to format and write your SD card.
Yeah eBay is sketch… I got mine off of amazon. I had the same issue with my other 64 GB card I got from a similar site. Its just black and says 64gb and I had the exact same issue that you did… Looks like you got shafted. For your sake I hope I’m wrong.