While Rock Auto does offer a wide variety of parts at good prices their customer service is non existent. Recently FED EX delivered my order to somewhere other then my address. Rock Auto has no customer service at all and the only way I resolved the issue was to dispute the charge which my cad company did and then Rock Auto responded. Since such things happen all the time I will not be buying anything from them again since getting any resolution from them is virtually impossible since they have no contact number or email which can be accessed in real time.
In summary there may be companies with worse customer service but I have not encountered them in the many years I have been purchasing items over the net.
Avoid them at all costs if you anticipate having any problems with an order..