When I plug a phone number from a non TER add into Google and it comes back showing multiple providers using it, is it an automatic red flag?

...Double check it by doing a TinEye or Google image search of the photo(s) in the ad.

From my own experience, I learned to just move on. Not worth the chance.

The multiple ads with the same number might not be a red flag on it's own, but it definitely indicates you should do more research. As xyz said it could indicate a legit agency or booker. Of course it could also indicate a pimp, scam, rob, or even LE sting. I would say more often than not, it is a bad sign but not always, which is why I would call it a yelliw flag and not necessarily red.

many providers (myself included) use google voice numbers that recycle rather quickly. I have let many providers use my google voice numbers when they pass through town so they could answer calls and not have to have an actual phone. They do it from a computer.

If the reviews are good, and are from reputable reviewers, you are probably good to go. If not, well then simply move on to the next girl on your list.

Guess it depends on your experience. It certainly could be an agency. But if there are no reviews for the lady in question, it adds a level of complexity to determine legitimacy. It also increases the chance of a bait and switch. Not to forget the other traditional rules.

If she is someone I am familiar with or a newer lady who's number leads me back to a familiar gal I won't worry about it and will probably think she's helping a new gal get started safely. However if she is completely unknown to me and the number leads to many people I'm more likely to look for someone else than run the risk of being disappointed.