I think one of the obstacle is the money transfer that people may be afraid of unscrupulous web business as they don't know the seller. Not sure whether credit card payment may help as it kinda gives a certain peace of mind if the transaction turns sour.
Also, it seemed to be the way of buying stuff in Thailand that you need to look upside down, inside out on the nitty gritty detail before you really pay for it. Mail order do not allow you to do so, right!
I think we should give a chance to good vendors with a strong track record. I have no problem in buying stuff from AVBestbuy with three transactions so far. I suggest the potential buyer to do research on this website first to see how each vendor does his business..
