I use PayPal to process payments and implement the shopping cart on my website. Recently I got an order that went through with the sales tax incorrectly calculated. So I tried to contact them to find out the cause of this issue, as this would be having a major business impact if it continued on future transactions.
My first attempt was via email, to which I got a reply saying that they have no access to my selling preferences, where the sales tax are set, so I should call a phone number to get better help. I called that number (long distance, no toll-free, FTW) jut to be placed on interminable holds and have suggested a ridiculous "solution", not applicable to the issue at hand. What pissed me off the most was the ease with which they brushed the whole thing aside, with no attempt to find the root cause of the problem.
I was pretty sure it was a bug on their side and what I needed was someone with some technical competence in investigating this. The good thing is that they have a developers' site, with a forum. Browsing through, I found a way to submit trouble tickets at https://www.paypal.com/mts. That's a very good way to reach the Merchant Technical Services. The nice thing was that within 5 minutes after my submission a reply came, apparently not automatic, acknowledging the issue and saying they are working on it.