Have you come across a successful etiquette for asking professional strangers to prove their vaccine status before engaging their services?

A number of people I know are working on the premise that they can’t transmit a Covid infection if they have had Covid, and we all know a few that think Covid is not a real health threat. I don’t want to see a professional for a close consultation if they have not been vaccinated. Is there an etiquette in place that you know of to ask to see their vaccination cards without causing offense?

Please don’t say “Just ask.” It is a volatile topic, people often react emotionally, I would like to avoid that if possible.
Please don’t suggest other Covid avoidance strategies, this is a very specific question about inquiring about proof of vaccination status.

General question