Coming from the other side the amount of s*** Chinese parts especially fuel parts like injectors and fuel pressure regulators is astounding and means we need to have a disclaimer for problems not arising from our work. Any tuner should stand by any work they do And parts they supply.
The other problem we are getting more and more of is people are buying project unfinished cars that have had 3 different owners, Chinese whispers turns it from being a rb25de+t motor to a fully forged rb25 will head studs etc. Its not financially viable for us to pull off heads to check so if we are informed that an engine is forged we treat it that way.
It also goes both ways, we have had many customers that try and drop car for tuning on 98 or npd100 then bringing it back a few weeks later down on power and surging etc on boost and we find 95 or even 91 in the tank because it was cheaper. This fuel grade clusse is in our contract but still gets ignored.