Probably worth mentioning along the same lines... avoid buying 'priced too cheap to be true' instruments through pawn shops and online listings. If it's too good a deal, it's TOO good a deal, and likely some poor musician got ripped off to make that low price possible. While there are certainly exceptions (inherited instruments sold just to get rid of them as not being played, someone really desperate for a few bucks and has to sacrifice at far below value for a quick sale, etc.), it's better to just stay clear. A lot of obviously stolen gear goes through craigslist and pawn shops, and police are mostly helpless to keep up with it.
Years ago fellow player in a community orchestra had his prized oboe and English horn stolen in a double case from his car, having left them on the floor in front of the back seat for about 5 minutes to 'just step into a store.' Combined value about $10,000. He haunted pawn shops for weeks, finally finding them both in one of those. The English horn had been modified, with two of the holes reamed larger and one new hole drilled. Apparently the pawn shop owner was a bit of a clarinetist, and thought it was an ill-made clarinet, so he went ahead and modified it to make it work... which of course it did not. Cost of restoration of this rare old horn: $3,000. Cost to buy the horns out of pawn: $50. Cost of picking up the case and taking it with him into the shop for 5 minutes, avoiding all this mess? Priceless. Thieves are opportunists. Leave something shiny sitting there and they'll grab it and run. Make it even a little bit difficult and most will just walk down the road to the next easy target.