For what people pay for plastic and aluminum parts for AR's, I think they should be damn near perfect. While I understand that most are made in the USA they are often priced as if they were one-of-a-kind pieces from a renowned artist, not one of a batch of a thousand made this month. If you charge $30 for a sling swivel, it should attach itself to your rifle for you. There should be no flash, no discoloration and it should fit like it was born there.
If your grip won't fit, have them send you one that will. $20 for an injection-molded piece of plastic that won't fit a standard lower is B.S.