1) Be very wary of carpet cleaning companies who say they can clean your rugs on site. Professional carpet cleaners typically use hot water extraction, hot water can bleed an oriental so if they do clean on site be sure they colorfast test the rug.
2) Do not let carpet cleaners clean oriental rugs if they do not have an rug cleaning facility. This is not to say your rug cannot be cleaned on site but if the cleaning company does not have a mini-plant and specializes in oriental rug cleaning, odds are they are not prepared to deal with the complexities of oriental rug care.
3) Assuming your professional rug cleaner has a rug cleaning facility, be sure they have specialized dusting equipment. Rugs can be washed over and over but if the dry particulate matter is not first removed it is very difficult for it to be removed during a pit wash.
4) Be sure their facilities have a drying chamber. Rugs are most often ruined by slow dry times than anything else. Even though a rug can be cleaned correctly, issues can pop up if just an extra day or two of dry time is introduced due to humidity or cold weather conditions.
Bonus tip: Even if a rug is cleaned at their facilities be sure all rugs are colorfast tested before washing!