I've learned at the various shows which vendors will be there that I like. I make sure that I buy something - anything from them to make sure they keep coming back. There is one woman from NE Ohio that drives 4 hours to be at a quilt show in March. I LOVE that she comes, she carries thimbles - and she's smart because she has sample ones that I can try on to see if they'll work for me.
And yes, the vendors change over the years. I bought my quilt frame from a vendor at a quilt show years ago - have never seen another one like it - even online. I'm sooooo glad that I got it when I did. At the same time, vendors aren't bring things like this quilt frame to quilt shows either and that's too bad.