If memory serves from one of my convos with a provider, RM requires them to send a picture of their certificate to verify they are licensed. That doesn't stop someone from printing out their own MS Word certificate, but it's as close as they're going to get to actually verifying the credentials, given the site's real purpose.
I mostly agree with poolboy, but I think if someone says they are certified I put perhaps slightly more stock in them ending up being a good masseur. At the end of the day, I think feedback I see here on the forum is more valuable than any listing of a certificate. My experience has been that the feedback guys post on here about the massage quality is always reliable... the extras people might mention are always taken with the YMMV caveat.