I don't normally grump about this topic, but like most of us I buy odd bits and pieces online – when buying from anywhere that isn't an established business my rule is only buy what I can afford to live without.
Sometimes I spot a 'too good to be true' bargain. Sometimes my fault, like the strap hinges that turned out to be sized for a jewel box rather than a guitar case.
Often turn out to be b-graded, like the R/C speed controller that had obviously failed due to problems with the original soldering but had been 'carefully re-worked' by an expert in hand soldering:

It works, but it's a moot question how many of those FETs are actually carrying their share of the current…
Yesterday I had four castors delivered, four for the price of one at the local DIY shed. One was looked solid – the centring bushes had been left out on assembly and the bolt tighted up until the side plates bent in and jammed the ball race. Cured with a length of ally tube and a couple of M6 washers, and a good price for a set of ball raced castors – but I assume the seller has got hold of a large batch that are cheap because an unknown proportion of them are QC fails?
And yesterday I dug out my insert tool for taking CCMT tips using the obtuse corner for a roughing tool. Again got very cheap … and realised why I hadn't been using it, the thread wasn't deep enough for the screw to lock an insert in place. Fortunately I finally remembered where my M2.5 taps and die are (Q – why aren't they with all my other taps? A-I was planning to make a box for them) and the work of a minute to fix the toolholder. I was worried about breaking the tap in a hardened holder but it went through like a knife through butter. Probably EN1a… actually good news because at 12mm deep I can skim it down in the mill to make it consistent with my other tipped tools.
Moral, if you didn't know it already, if it's online and so cheap it looks to good to be true assume you might have to do some remedial work…