Working as I do in a technical capacity, one of the things that often strikes me is that there is a level of knowledge that is often more dangerous than others. This level seems to be simultaneously both too much knowledge and not enough knowledge, and usually consists of someone knowing enough about a subject to have picked up some of the technical terms, but not enough to fully understand the subtleties of them. The end result is often a request that looks reasonable enough at face value, but if carried out to the letter will result in either an incorrect out-come, or on some occasions the exact opposite of what is probably intended.
The trick is to spot these requests and ask for a clarification of the intended end result in such a way that doesn’t upset or annoy the customer – or end up further confusing the issue (and yourself – more common than you might expect!).