Is there a polite way to ask a provider about the status of her health? Obviously there is an inherent risk in the hobby, and providers could lie (perish the thought), but, is there a good way to ask her if she has something I wouldn't want to catch? Or, would I get lied to as it would be bad for business?

If a woman is still providing knowing that she has a disease and could transmit it, I highly doubt that she will tell you the truth if you ask.

Like you say, not exactly good for business.

Make sure  you have YOUR health certificate in hand when you ask her! It would only be fair!

You don't.

If a lady has something you wouldn't want to catch, why would you believe her to tell you the truth?

Until and unless decrimilization or legalization is in place, few ladies would be willing to show you a health certificate with her real name on it... and what good would it do to see an anonymous one?

Assume that EVERYone has something you wouldn't want to catch, know how to spot obvious symptoms, know your risks (spend time at the CDC website), play according to your comfort zone, and don't forget to have fun!!!

That is actually the first time that has ever happened.  I politely declined and told her that I trusted her.