PM with other members on whatever local board applies. Over time you will build a little network of people who can give you input about who is good, who is reliable, etc.
Not that I take PM info on NCNS too seriously. There is a highly rated provider in Chicago who has a reputation for going NCNS, but most of the reports are via PMs. She works a lot and I am pretty sure the reports are valid. As the OP said, shit happens. Some of it may have been that something came up, and at other times I think she got a better offer - either way, there have been times when she left guys hanging.
But I saw her twice and both times everything went as smooth as silk. And I am hardly alone - she works a lot.
On the other hand, I had a comical NCNS experience with a now-disappeared provider who stood me up about 6 times, each time apologizing profusely, giving me a new story and promising to make it up to me. And I took her seriously the first two times. After that I just kept doing it for amusement, and then when it got boring I suggested we take a different approach, one where she had to prove she was serious and then the communication ended.
PMs about her revealed lots and lots of similar experiences, and while she seemed to have her share of admirers on the local board, and a couple of reviews, as far as I can tell she flaked out a lot more often than she showed up.
The message on each was fairly clear if you read them carefully - provider 1, there was some risk she would NCNS, but it was likely she would deliver; provider 2 is flaky as hell and you should just avoid her.
So there is a way and a value to you and the board to communicate the provider's NCNS, but do not exaggerate it, just state the facts. And I assume you gave her a chance to explain what happened (hint)? Not that I would try to see her again - the best predictor of future behavior is past behavior, or fool me once... As with my provider 2, the more dangerous lady is the one with the ready excuse and easy apology, because she has lots of experience in that situation.
zig