Hard drives and motherboards have all been failed components so I never purchase those anymore, I made the mistake of storing them until I needed them for a new build. Now I only buy components that I will use straight away so I have a chance to resolve any issues.
Apart from one recent purchase memory has always been good, but I have usually only bought smaller capacity sticks that people don't want generally. It is better to avoid larger sticks as often they are being sold as they are faulty, just like the hard drives and motherboards.
CPU's have so far always been good as have graphics cards, but again I have tended to buy models that are no longer in vogue. Chances are something really sought after may be being sold due to a fault.
Before bidding on components check the seller feedback carefully, if they have not got any positive feedback for a sale in recent months they could be a scammer selling defective parts. I didn't check the feedback when I bought memory (which in my experience won't stop working when removed from a machine) the seller asked me for positive feedback to be sent as soon as I received the item. When I went to test it was a slightly different size to standard ddr2 and would not fit my board. I asked for a refund and was refused as the auction said no refunds. He opened a case against me for negative feedback and got it removed, I opened a case for a refund.
He was adamant that the memory was fine so I took it to a friends house and tried it in his computer. Surprise, surprise it didn't work, I mentioned this in my case but was still refused a refund on the grounds that I must have messed it up by not wearing an anti-static strap. Last weeks issue of Micro Mart (breaking myths) proved that since we don't have nylon carpets anymore anti static straps are a waste of time.
I got bored closed the case as it was only about £12.50.
The point is the guy has 99% feedback and a 200+ rating but only one positive in 6 months for something he purchased. Ebay removed my negative feedback so how many other people has he or others done this too?
Memory doesn't just fail, I was had.