i am by no means an expert on exhausts but I'm sure someone will have further input on this and correct me if I'm wrong but I'm sure i've read on a thread a while back about certain eBay ones being fine but its down to which one you choose to get as some have bigger flexi pipe in which is better? Something to do with causing less pressure on the welds etc?.. Therefore less likely to have any problems with welds cracking as mentioned above..
like i said.. I'm no expert but someone may add to this that knows more about these things than i do which will then give you something to think about when looking..