Bad experiences that have me cross a shop off my list include-
Retailers that have a website that offers a product, indicating it's in stock when it's not. They allow you to order it and wait for weeks for it to arrive leaving you in the dark. When you contact them, only THEN do they inform you it's back ordered. They're unwilling to be honest upfront because they figure a certain percentage of customers will just wait for months without asking questions.
Retailers who have a three, four, or five day "processing" period. If Harris can process an order in mere hours, have instant information on the stocking status of an order, and give accurage shipping estimates, why can't others?
I've done a TON of online shopping and have done business with most of the major retailers as well as a lot of the smaller ones. I'll back up the other recommendations for three sources which seem to consistently offer good prices, good selection, and reliable, quick shipping-
ebikestop.com
harriscyclery.com
Lickbike.com