Having done this for a while, I've come to the conclusion you can't really make any conclusions until you meet the guys and jam. People will always have some type of shortcoming, so it's a matter of what you can live with. That's why finding a fit is so important for a long term project. In the end, a red flag is only a limitation, and we all have to live with limitations. I surely have plenty of limitations, but by grace I seem to find work. It's more a matter of fit.
But you don't want to waste time either.....
The #1 thing that I have found to be a good indicator of a band's potential is a song list. If it's an original band, a body of work such as recordings. From that you can determine if the material is something you would enjoy doing, and it shows they have put in some kind of work and planning.
The #2 thing is a phone call. It helps if a band can communicate and get along. You can't jam by text or e-mail, so you'll actually need to talk sooner or later. I find this to be a good screen.
If these 2 things jive with me, I'll go audition. The last time I did a bunch of auditions a couple of years ago, I asked for a song list. I did about 5-6 auditions, and none of them were time wasters. They were all bands that were playing out, had decent gear, a place to rehearse, material learned, etc. Nowadays on the occasional audition, I will still use those 2 criteria, and I still haven't had a waste of time.
For me, just because it isn't a fit, I don't consider it a waste of time. As long as I met some cool people, jammed some cool tunes, and didn't cost me too much, I consider it a positive. You don't always get a great fit, and it's not always a fault of the auditioner or auditionee, nor does there need to be a fault. People have limitations, and that means that there will be bad fits.