When I started I only offered OW, but I found the condoms so off-putting (primarily the bobble on the end, which triggers my gag reflex even with a tiny cock) that after researching the relative risks I decided to offer OWO.
It's up to the individual what they are prepared to do. As long as you make it clear in your advertising that oral is protected only, then clients can't complain.
BTW if a guy has a smelly or dirty cock I ask him to either go and wash, or I can use a condom for oral. I've only had to do this once and that was a guy who was disabled and had trouble cleaning himself thoroughly.