Is it a used one you can handle yourself to check for quality, and to make sure it's been reset (e.g. their account was removed)? If so and if the phone is in reasonable condition then maybe you can get yourself a bargain. But if you are looking at eBay, etc. and can't inspect the phone first at least try to make sure it's from a reliable seller and ask about their return policy, as a lot of things can be wrong with a used phone that you can't personally inspect.
I actually bought mine from Motorola this time (I bought the N4 and N5 from Google), as I found their 2 year insurance to actually be fairly reasonable since I prefer to carry my device in my pockets without a case (IIRC it was $100 for 2 years protection, $30 deductible covering broken screens and water damage, and could be used up to 3 times in that time period). Not that I plan to use it, but considering the investment I ponied up for the extra coverage.
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