You regret that when you saw her ad re “precautions” you didn’t ask her for specifics.  

Then you leave.

If it was high enough to be concerning, I'd probably go home "just in case" I really had something, but if it were under a hundred I'd be calling my local K-Girl agency before I even turned around to leave and I'd be asking for the next available session.

 
Always have Plan B.

If I test positive for covid, I go home and quarantine. If I test negative, I notify the lady and offer the paperwork as proof that I'm safe. If she still refuses to see me, I move on to another girlfriend.

A lot of these thermometers are less than well calibrated. Maybe also review the instructions to be sure it was used correctly and then retest both of us.

Still, at the end of the day I probably leave (with my money), even assuming the the thermometer is something of a scam what are you going to do, rape her and claim it wasn't because you paid?

Move on and make alternative arrangement.

But for those that find themselves unbearably indignant about the situations and feel they must write a review. Well, leave your money and then write a rip-off review.

and if high, I'd get a COVID test.

I check my temperature twice a day already.  It's so easy with the digital thermometers.  Doing so would avoid the scenario that you describe.

This was a REAL problem at at least one of the infected meat packing plants in the midwest. After there were already a lot of infected workers, some places implemented testing: check the workers' temps before letting them in to work. If their temp was too high, they were turned away and sent home.  
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Some workers who KNEW that they had signs of fever / elevated body temp were taking aspirin or other over the counter antipyretics to lower their temps. That got them in to work where the spread continued. At some of those places, if you don't work ONE day, you are replaced by someone else and then you go to the end of the line of people waiting for work. I don't know the status of the worker paycheck protections at that time. For those for whom it is "work or starve", they don't always think about the larger ramifications of their actions.  
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If you have a temperature or other symptoms, DON'T MESS AROUND with other people by trying to hide the fact. Take a break. Shelter in place. Quarantine. Think of others, not just your own libido.
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New TER Poll: Are you Celsius or are you Fahrenheit?

Turn around and leave. As long as you didn't pay for the session or if you did and received your refund, it's fine.

It would be better for the provider to actually write that they will take temperature at the door. A corg in the bay did this, they straight up said they will turn people away if the temperature is too high.  

Does it suck ? Yes. Still, I can't fault them for trying to stay safe. Even if I question the method (covid travels so well and there are so many asymptomatic cases, it will find a way), I can't fault them for trying.

A word of caution for those who take blue pills: those do lower your blood pressure and increase (at least) skin temperature.