There’s no foolproof way of spotting it. Find a reputable detailer near you, read their reviews and talk to them, ask questions. If they’re passionate about it or have a very good reputation, they wouldn’t damage it by trying to save some money.
There are a lot of untrained technicians who have recently opened outlets only with the intention of making a quick buck, they are not really in for a long term goal and will vanish quickly by offering dubious warranty, guarantee schemes that are irresistible in the beginning and vanish before you even realize. Our suggestion would be to stay away from people who claim – 10h, 12h, etc…, several layers, Hybrid Ceramic Spray Coatings, Claiming to be manufacturing their own coatings, or brands that do not have a presence anywhere else in the world, apply once and forget and such sorts. Another thing to look out for is people claiming that a ceramic coating gives shine to the paint, it’s the intense preparation that goes before it that gives the paint the shine and gloss, not the coating itself.
Opt for a professional always who has a good reputation in the industry, ask technical questions to know whether they know what they are doing and a bit of homework would put you in a better position.