Dead Right Tony , Kevin and all others concerning second-rate replacement parts. There are some very good copy parts out there , but there is an awful load of crap. The problem with the parts suppliers and motor factor chains is that they have no real technical backup. They buy a batch of parts from a reliable source one month , and then their buyers will be offered what looks like a similar part a little cheaper and next month they are selling rubbish.
On one occasion we had a batch of genuine manufacturer original parts which we offered to one of the parts companies because we thought they may be interested. They said that they would only buy them if we removed the vehicle manufacturer's markings and supplied them at the same price as the garbage they were buying already so that they could change supplier easily if they were offered a 'better deal'!. I am not going to mention the name of the company but this is what users of these parts are up against.
Another problem is counterfeit parts and more commonly counterfeit packaging. We have seen junk (mostly from China) in boxes that are indistinguishable from Bosch , Ford etc. It is easy for a parts buyer and then his customer to be fooled.