I would suggest you do a little research on brand and original cost and then consider if they posted a picture with it. There are, of course, people out there that will try to rip you off, but there are a lot of honest people also - some just moving up in the hobby and needing more room or a bigger tank or maybe leaving for college. I bought a 26g tank from Craig's list with stand and a bunch of equipment and supplies for $100. It is a very nice unit and he had cleaned it up well. One thing to be sure to ask is what they used the tank for - some people don't know that there is a difference between fish and reptile tanks and though some get away with filling a reptile tank with water, the glass and seams aren't as strong. Good Luck!