There is a parallel theory that follows as such:
Ugly prostitute = Less customers = A need to retain whatever existing customers = A higher
likelihood of her engaging in unsafe practices as this may be the only selling point that she
has in a huge market of better looking prostitutes.
Just a theory like yours bro (there are many others). But whatever the case, the reality of
the situation that there are always risks associated with doing it with a WG, pretty or ugly
(which leads me to another point, looks are subjective to the punter and i am sure there
are WGs who are more appealing to some punters than others).
"Wrap your tool" is the best theory out there i think.