I suppose there's always a risk but if it none of us would take the chance of unprotected sex with a wg, and none of the wg's we would punt with would take the chance of unprotected sex but she may have entertained a punter that may have had unprotected sex at some point with another girl then the risks are minimal, even without their regular health checks.
I don't know the statistics but I would imagine more std's are transmitted between people where a financial transaction isn't involved, outside of punting how many of us have never had unprotected sex, ever? It's good to be cautious but this level of forensic investigation seems a little unnecessary, just be sensible about your own conduct during punts.
As a relative new user of UKP, and given is broad usage amongst punters and their honesty, have there been many std horror stories?