Absolutely true. But how do we protect ourselves? If the provider has the virus, we're pretty much sunk. I don't think any of us are going to ask the provider to wear a mask. Or even tolerate it, if the provider shows up with a mask.
Some of the usual precautions (touch as few surfaces as possible, wash hands, don't touch face) will help protect us from the previous customers, but if the provider is infectious, we're probably going to get it.
The best situation we could hope for, short of a vaccine, is that the provider has already had the virus and recovered. (I realize there are still some uncertainties there, too.)