for those not used to buying slabs at coin shows:

Genuine slabs have a company name and a serial number so you can go to their website and verify the coin's authenticity. You still must beware, though, because the Chinese have counterfeited the slabs from legitimate grading companies.

Always carry a magnet at a coin show. It's the simplest first test for counterfeits. Also watch for slabs that can be peeled open. But in any event, buying an unmarked slabbed coin is no different from buying a loose coin: it has not been legitimately graded.

I was burned on Ebay, but was able to get a full refund. Options are limited at coin shows; it's a good idea to get a business card with your purchase so you can at least report it to the show sponsor.

If you look at Alibaba or Temu's websites, you can find counterfeit coins very cheap - as well as counterfeit U.S., Euro, & British currency. "Counterfeit" was actually in the Alibaba search terms last time I checked. That's how some dealers make their profit, so beware