I probably should be more specific and say that I've been duped a few times, and some of those mistakes made it into kits a time or two. There was a time period 10 or so years ago where the little 431 regulators we use just weren't available for a long stretch. There were some available on eBay labeled WS431 that looked to be acceptable substitutes, but man were they noisy! Likewise I grabbed up what looked like a good lot of UF4007 diodes labeled with the band name "TCI", and they don't meet spec (currently I use them for super low voltage/low current rectifiers). I think there were even some 2N2907 or MJE350 transistors at some point that were also dodgy.
If you're buying on eBay, you have to look for stuff that looks really old and is packed into old looking packaging (boxes or faded plastic packaging from a retailer).
