You may have power leveled months or even years ago and never have thought twice about it. You ordered the service and you got your character back and it was fine. You might even be thinking of buying another service - but don't.

What has changed since then? 9 months ago Blizzard did not have any automated detection methods in place to thwart powerlevelers and gold farmers. In fact I have reason to believe that up until about 3 months ago they were only using manual investigations and bannings because they would need quite a large workforce in order to weed out 100,000 accounts out of 8 million.

With the advent of IP-tracking and Warden, currently almost all bannings are automated or semi-automated, at least that's how it seems (seeing as powerlevelers get banned very quickly, while some legit users complain they were unrightfully banned.)