Probably lack of website advertising "escort" and offering a list of "GFE" services.... Lack of reviews... Knowing the girls real name might come up instead of just "Lexus" or "Jasmine"... In SB stuff I generally either know from her telling me or through research found her real name. I don't always tell her I know right off the bat but I keep it in my mind if any questions come up. If an officer asks you her name and it doesn't match whats on her id then it will throw up a flag. Escorts attribute a specific amount of time to a specific dollar amount. SB relations not so much, but there are a lot of SBs that are getting that hourly mentality.
SB relationships if used in the way they are intended it is more of a GF/BF relationship. However a lot are more short term or medium term quasi escort flings.
Like they say, it isn't illegal to have sex, it isn't illegal to give money, but mix the two then the shit hits the fan. Kind of stupid really. In a lot of ways keeping it illegal controls the proliferation of it without having to spend tons of time/money regulating and licensing. It sort of keeps it underground for the most part which can be good, and bad.