I do electronics as a hobby. I sometimes buy chips from very dubious shops in China for fun. Some of these sources are sketchy even by Taobao/Aliexpress standards. Then I decap the chip by boiling the package in acid and inspect the die under a microscope. More than half of them are genuine. I get some nice surprises because even the chips that I expect to be absolutely fake can turn out to be genuine.

So far I've seen a ton of fake audio op-amps.

For discrete parts like transistors things are much simpler. Just build a simple test rig and test a few parameters. If they fall within the specs they're probably good enough. Of course it's not worth it to do this for jellybeans like 2N3904, but when some parts get obsoleted without a replacement (or they're too pricey) there isn't much else a lone hobbyist can do.

Not so with power transistors, you don't need a microscope to see that the dies found in off-brand power transistors are suspiciously small compared to equivalents from proper manufacturers.

they also may be refurbished ie unsoldered off a board. that happened to me a few years back for a bunch of soic op-amps I was having difficulty sourcing.. they worked ok though.

> Some of these sources are sketchy even by Taobao/Aliexpress standards.

Links? That sounds fun...

I've bought hundreds of electronic parts on eBay and rarely had issues. I discovered LED strips were a thing by shopping on eBay, years ago, much before they were trendy, I was buying them at one fifth the cost American retailers were charging. Bought Arduino clones for a quarter the price of the "real" thing when I was a broke student. ATMega MCUs for a dollar a piece, free shipping. They worked perfectly fine. Could not have afforded them without eBay.

I'm Canadian, and last I checked, the shipping costs to get parts from places like digikey was just ridiculous.

I didn't say they don't work, just that I don't expect them to work. The prices are such that you can, and should, buy three items from three different vendors and cross your fingers that one works.

In professional engineering, where time is money, Digi-Key or Mouser is always more efficient, if they've got what you need. For personal stuff, where the value of your time is ~zero, the opposite can be true.

99%+ of my hobbyist electronics bits n' bobs are ali express/banggood specials, and they have all worked fine, from arduino clones to sensors and ESP8266's.

If I were working on something more important that dinking around for fun, sure, I might care a bit more about what's actually on the board. But as it is, the clones are more than adequate for my needs, particularly at their price point.

In the case of the ESP8266, the parts were available through channels like eBay and AliExpress long before they showed up through any of the typical electronics distributors. Same thing goes for other first-in-China parts like the GD32 series (STM32 clone) and WCH340 series (USB/serial).