IMO, if you are in the loop with a number of businesses, say VW parts or repair, Porsche service/parts or any other 'circle' whare ppl share info, soone or later you will hear bad about every one of the vendors in the group. One has to judge the severity and frequency of the complaints and the ratio of 'good' rumors to 'bad'. Then you try the ones that seem best and then go with your personal experience.
As Dave said, it really is the way problems are dealt with, not the fact that they WILL occur.
I've never dealt with IMPEX as so far thier prices have been beaten elsewhere with a similar level of service. Isolated, trivial complaints like this will not stop me from trying them in future if the spirit (or a sale) moves me.