I have for years accepted bbbj and rimming - much like buying a camel you need to check lips, tongue and mouth . I take a good look at a gal before we engage - a good place is immediately when you walk in as it’s brighter and also in the shower - also brighter .
In real conditions it's just too difficult. The human eye is not reliable enough to determine all but the most severe cases. Minor cases will not be detected.
This is why the microscope was invented.
A better gauge is repeat visits and analyzing her behavior and traffic patterns. For me I've only done anything raw with a legit provider who I was personally referred to by a Mamasan.
Age is also important. Older providers are less likely to have lingering asymptomatic infection because with age you see the Doctor more and there is a higher chance of them catching and treating or at least them being aware of any Hepatitis infection.
A young girl is more likely to end up in situations where she's drunk and doing stupid things which includes Lesbian activities which is also obviously a source of STDs - Monger #322 with asymptomatic Gonorrhea blasts in her friends mouth and her friend licks her cunt at the Karaoke bar and then you go in raw a week later right before symptoms begin.
Sounds unlikely but I've heard of stranger things.
Everyone has their own risk tolerance. Bottom line check her volume and the nature of services she provides as well as her age.