I would say that one of the most important factors when visiting a spa is how organized they are.  I personally love it when I go and feel that they are paying attention to my where abouts in the spa.  Say I have three services, I want each therapist to know my name and know what I like from previous visits.  Natural Body has earned my business this way.  I must say they have come along way since I firsted visited them in February of 2002.  Just a better flow than before.  Okay, enough said they have my endorsement.
I hope this helps out.
Pros:  Flow, Attention to detail, Knowledge
                        
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