Any vendor can unknowingly sell a defective product. It is how they handle the followup that is in my opinion what counts. So when I got my RMA for my problem parts I explicitly asked about re-stocking fees and was told there would not be any.
GUESS WHAT? And ECS was unable to explain to me where MY money went other than to them. I spent way too much time trying to explain the situation to a CSR who I am afraid was a bit slow and after a slew of emails that got nothing HERE WE ARE!
So they have been around a long time and undoubtedly have many satisfied customers.
Summing up my experience it would have been far easier and cheaper had I gone a Mercedes Dealer and paid retail for the same parts.
You pays your money you takes your chances.
NEVER AGAIN FOR ME