I wasn't offered it despite being clear what my profession was, but upon asking for it I was given the jab. I think you do need to arm yourself with info as I have a suspicion they are watching costs.
Also agree with Dani, be upfront as mine offer me appointments, plus if I want to be seen last minute they will see me very fast. On my first visit, they were very good and run through some steps that help stop the spread of STD's. They were common knowledge to me, but may not be to everyone.
Without sounding patronizing (hopefully), it is always worth asking them to show you exactly how to put a condom on. When clients have done it themselves, it is laughable, they have no idea. So I'm sure the same goes for a percentage of us girls.