a woman in a "normal" job in your workplace, church, shop, supermarket, block of flats, or who is your neighbour could have HIV, and look healthy.
Or have herpes, chylmadia, etc.
Whilst it's possible that WGs have STDs, I think most do take care, and a lot do post actual medical STD results.
The only real way to never get any STD is to be celibate for life. the least risky way is only ever have sex in a marriage or relationship, but even then the spouse could cheat, or lied about past sexual experiences, etc.