I used to play darbuka a lot. I would look for the following things:
Heavy, cast aluminum rather than a thin aluminum shell. For the price they're asking, this should be a heavy drum, with a shell as thick as pottery but made of cast aluminum. If it's a light, thin shell, the price is too high but the drum might still be perfectly fine. If it's cast aluminum, the price sounds pretty good, but it's been awhile since I bought a drum.
Cheaper drums are often flat, like the "Turkish darbuka" shown in the smaller images. Of course, plenty of people play the flat-head drums, and I did it for awhile, but I've seen plenty of bandaged fingers as well.
If the head is glued on, you're going to spend way more time than you might enjoy heating the thing with a blow dryer or setting it on a heating pad to tighten it up, and you won't have fine control over the evenness of the tightening.
Before you test the drum, you might look at one of the YouTube videos on playing Arabic style to see the hand movements required to make sure you're pulling out the best tones that the drum can provide. Then, when you test it, there should be a clear difference in tone between the center of the drum and the edge. If the drum is cast aluminum and the body is covered in possibly hideous fake leather, this is actually good, in my opinion. It gives you some traction and helps keep the drum in place.
That's about all I can think of right now. Have fun!
