You're indicating that it's safer to shag a random woman you've met down the pub, than a prostitute. There is no difference. Unprotected sex is just that. Unprotected and carries risks, no matter who it is.
How do you know a WG you've seen hasn't done BB before with someone else? You don't unless she advertises the fact, or offers it to "select" punters she thinks she can trust. Her partner may well sleep around and do BB with others. Just because she hasn't offered it to you, doesn't mean she hasn't done BB at some point in her life with someone else.
Why are you twisting the discussion? I was talking in the context of covered shagging with a known barebacker (as per nixon81's experience) not unprotected sex (penetration). Perhaps I should've been clearer that the risk (for me) comes from oral transmission (kissing/OWO/CIM/RO).
I believe the risk (of contracting something orally) from covered shagging a random woman I've met down the put is lower than a from prostitute
who offers bareback. On an individual basis, of course risks will vary wildly: one civvie might be a suitcase of disease and a SP might be very careful about how she conducts herself, but on average you're putting yourself more at risk with a known BBer.
The rationale is that known BBers are likely to shag many more men BB than civvies. These men typically are barebacking other girls (civvie and working). The likelyhood of disease transmission orally is higher IMO.
