I've bought 4 engines, extra clutch pads, extra carberators, extra chains, exhaust pipes, and extra sprockets from boygofast, and i have not had one problem with any of the stuff. Nor have i had a problem with shipping, customer service or anything like that.
I have always gotten my stuff 2-3 days after ordering from him.
all 4 of my engines run great (2 are mine, 2 got put on friends bikes).
no problems here, but that's not saying that every once in awhile someone will have a problem or get a lemon engine.
That happens no matter who you buy from because it's the luck of the draw.
paying a higher price may get you a warranty, and probably phone support if you need it.
I have never needed any support so i have no idea how b.g.f. (or anyone else) would handle that type of thing.