I've bought parts from him, most are priced decent in my opinion but I don't shop at ChinaMart so perhaps my threshold is different than those complaining.
I think about the effort a person like him has gone through to locate these original parts, build a warehouse to store them, advertise his business and go to all of the events to offer these parts to people looking for them. I would say he was gouging if he bought the parts for next to nothing and sold them in his spare time out of the back of a rusted out van but he has created a business and deserves to make a profit just like you or the company you work for does.
Most used stuff is restorable IF you can find someone that knows what their doing AND gives a s**t restoring your part but usually it looks like a restored piece of crap. I know, took 3 times to get my last bumpers done right and all I heard was they were the best they could get them until they finally did them to MY satisfaction. Try and find someone that replates pot metal nicely.... good luck! Most aftermarket is just crap, maybe it fits, maybe it doesn't and I can usually spot it fairly easily on the cars at the shows. And most of it is made overseas, know why? Because you'd whine about how expensive it was otherwise.
There is a difference between a $10K restoration and a $40K restoration, just because you can't afford the latter doesn't mean it isn't worth it to the guy that can. I don't ***** about it, I just look for the part I CAN afford.