As an SL photographer, I can say even I, myself cringe when I see some other photographer's work. Especially because I know how the process works, I can see faults perhaps the clients wouldn't. I've seen legs melting into eachother (bad shading), jagged edges (no anti aliasing), too much light effects to make up for what the pic lacks (although I'm guilty of that sometimes, i love light! lol), unrealistic fake shadows, i've even seen once from one of the most prominent studio in SL, the worst mistake: BAD resolution! Yes, pixelated avatar......i've had clients come to me in complete anxiety over their past experiences with other studios but thankfully they enjoyed the photos I made them, and restored their SL photographer confidence .
The list goes on..
I think the best photographer you can get your hands on, would be one that gets isnpired by your photo and talks freely with you about their inspirations and exchange thoughts and ideas for the photo. If they're too silent, pushy, or rush things, definetly don't continue with them and demand a refund for your deposit.
Of course that might hurt the shy photographers out there, so weigh what I said with their portfolios.
It would be ideal if the client didn't have to pay a deposit, this way you could get a test shot with the photographer and see what their work really looks like, and pay when you've approved it. However, from a photog point of view, a broke client could just take a snapshot of the photo when its displayed to them for approval and say they dont like it, then walk away with my work and I get nothing lol.
It is complicated...sigh. Well, good luck .
A tip for photographers having a hard time with gaining trust from their clients, I would recommend using software like fraps or camtasia studio, and do a speed edit video of your edit and upload it on youtube. It shows you really did it and plus gains your popularity and exposes you further on the web for further bookings :3. Since it's fast forwarded, you're original editing techniques won't be easy to see (in case ur special or something hehe), but the process itself is cool to watch!