1) It doesn't have to be harmful, actually. It can be hilarious. As in, take-this-sentence-wildly-out-of-context hilarious.
For me, the horror of a bad translation isn't really the inaccuracy or the stilted use of the output language's vocabulary or even the sentence structure, but the unedited and direct translation of run-on sentences that the Japanese are habitually prone to, and these are incredibly long-winded and confusing. Stop the train I wanna get off destination where ahhhh
2) Time devoted to making it a very nice read. It's hard work, but some professional pride still goes a long way
3) I wouldn't look for telltale signs despite everyone's say in it, but if you don't understand the basic premise of the VN, it's usually the translator you must blame for that. It's just bad to not understand how Japanese works (or to have never watched anime or J-dramas your whole life) yet be the translator.
(As an aside, cokesakto is a primitive example of bad translation in general)