Summit/Jegs seem to have standard policies of up front customer satisfaction/verification of part#, shipping price, etc, but mancini's seems to be stuck in the stoneage when it comes to customer service details.
First impression is everything, and I think they have the attitude of "Build it and they will come", but in todays world of competition, it is a cut throat business that thrives on beating the other guy with exempliary customer satisfaction.
I don't know much about the details of their operation but mancini's seems to run their business like a hobby instead of a competitive business.