My personal suggestion is to find out what are the bands that the studio has done recording for. Go and buy a few and listen to the sound. It helps to get the same genre you are going to record. If possible get in touch with the band and find out more info from them (like cost, experience).
You can also get these 'samples' cd from the studio direct. But always bear in mind, if someone were to sell you something, he will surely show you the 'best side'. Again cost is often tied to what is to be produced. If the sample actually cost $20K to produce and you are looking for $5K package, obviously you won't get a $20K quality job.
Lets say you done your research and you negotiate the sale (this is still like buying something). Always cover all the grounds, especially the costing, the work involved and the final sound you are expecting. It also help to let the engineer hear some demos you done to guage if he can do what you expect.
Different engineer will give different output, some good, others not so good. Sometime raw sounding album could suit the music after all too. It's all very subjective. A dirty sound is not necessary a bad sound, just look how dirty guitarists want their sound to be, infinate possibility.
It's just another life experience, sometime good, sometime bad. So be pragmatic and realistic, just like buying durian.