Well, at the risk of sounding different, my experience with Diesel has been very good.
I have bought books from them and when I did have a problem (once), they responded quickly and took care of the problem.
From a pricing standpoint you are credited back a portion of the purchase price (BooksOnBoard does this as well), so on that basis alone their price often ends up less than Amazon, B&N etc., especially when it comes to "Agency Pricing".
My experience
