Bought a used car the seller said had ceramic coating on it - how can I actually tell if it's still there?

Your description acutally sounds like there IS some coating left on parts of the car. A truly bare, uncoated vehicle almost never beads water in tight little blobs - bare paint wets out and sheets off flat. Uneven behavior panel to panel is relly common on a coating that's a couple years old, because the horizontal surfaces (hood, roof) take all the sun and rain abuse while the sides stay protected longer. So patchy isn't a red flag, it's kind of the expected wear pattern.

The fingertip test on wet paint is legit but takes some practice to read. Wash the car first, rinse a panel, and drag your fingers slowly across it. Coated paint feels noticeably slick and squeaky-smooth, almost like there's nothing gripping your finger. Bare paint has drag to it. The grippy feeling you got could mean the coating is mostly gone in that spot, or it could mean you picked up contamination - tar, rail dust, old wax. A clay bar pass before judging makes the test way more reliable. A couple other easy checks: after washing, watch how the car dries. A working coating makes water roll off in beads that stay round even on a drive around the block. Bare paint leaves a full thin film of water that air-dries into spots. Also look at how dirt behaves - coated cars stay cleaner longer and rinse clean easier. You don't really need a shop with a paint gauge for this one. Those thickness meters tell you if paint's been sanded or filled, not wether a coating is present - a coating is only microns thick and won't register.

Practical advice: wash and clay the car first, then hit one panel with a spray sealant or spray ceramic product from any auto store and see how the rest of the car compares. If the sealant panel behaves dramatically better than the hood, you've learned the existing coating is shot. Honestly, at two-plus years with unknown provenance, most people would just decontaminate, polish, and lay down a fresh coating rather than guess. Starting clean means you know exactly what's on the car and how old it is.

Bought a used car once with the same 'it's coated' claim and it turned out to be a spray wax the dealer slapped on. Faded in like two washes. If the seller remembers where it was done, one call to that shop coud settle it - most places keep records even a couple years out. Also, don't forget the roof and rear hatch when you're testing. Those get baked the worst, so if anything survived it'll be on the doors and fenders. If the sides still feel slick and bead hard but everything horizontal is done, that lines up with what was said above about wear patterns.

Agree with calling the shop if you can find out where it was done. I bought a used wagon a while back and the seller had zero paperwork, but when I rang the detailer he remembered the car and even emailed me the invoice with what product they used. Took ten minutes and saved me from stripping a perfectly good coat. Worth asking the seller for just the name of the place, not proof. Most people remember where they spent that kind of money even if they lost the receipt.