For my hobby / fiddling stuff, I buy components from "the usual scumbags" - direct from China. Occasionally you get duff components or an outright scam. Most of the time it's fine.
But I wouldn't trust those parts for anything serious. When I needed to repair the board in my furnace, for example, I ordered real name-brand components from Newark (Element14 and other names elsewhere).
The good stuff does cost 10x or 20x as much, of course, so it's not great for hobbyists.