I have a few used that I bought many years ago. They are fine, and in fact, better than several I got as gifts.
If you do not know the name brands to look out for, or what to visually look for in the photos, such as joinery, wall thickness (holds humidity better), telltale signs of cedar laminate vs solid cedar, Hardware and build features within a makers lines (for instance, the cheaper lines may have hidden leaf hinges while the better line has quadrant hinges), etc., then stick with someone who offers an ironclad return policy, and know that you have the time and energy to do the return.
You be patient, and scan new listings everyday. You'll possibly find something nice, and probably save up to 75% if you know what you're doing. I paid $125 or so for a nice $500 humidor.