Ways to spot fake NGK spark plugs

During periodic maintenance at a garage, I got misfire errors after the spark plugs were changed. When I took it to the same mechanic, he said things like 'your engine is done, the engine needs to be scrapped.' When I went to a different mechanic, I found out the problem was the spark plug and got it replaced. But the plug that came out was different from the one we bought — especially differences in the print, the gasket coming off by hand, and machining marks on the metal part from imprecise manufacturing. Has this happened to anyone before, and can anyone recommend a reliable parts dealer in Istanbul?