I have three used tanks - one from my lfs, one from a member of this forum, and one from craigslist. All are in great condition and all but the one from my lfs were really good deals. I payed more for the 30 gallon from the lfs than I did gor the 56 I found on craigslist. I will soon be picking up a tank I got for $35 at a thrift store, but as I haven't seen it in person yet I can't speak on its quality yet. As said, look closely at any extras. That's what can really make a good deal. And check for damage or leaks.