Some of the best customer service I've got was from horticulturesource.com, they answered all questions clearly within a few hours. Their shipping charges (you can calculated right from the website) for some items may not make it worth it to buy from them, but the prices of what I was after were fair.
The worst customer service I've ever got was from progressive-growth.com in BC, Canada. Horrible. Eeverytime I emailed them got no answer, almost every attempt to call was told to call back because the person in charge of international orders apparently is never there, the person who answers the phone always appears extremely unmotivated to help you purchase from them... it's almost as if they want you to beg them to make a purchase. Fuck that. I tried to get some items from them because of cheaper price/availability but gave up on them. Will never order from them again.
Another place that my bros use that is really good for international orders is "the hydro source" on ebay. The dont have a very big selection, but prices are a little cheaper for most items and we've had sucessful deliveries everytime!