where should we look for or post if we are skeptical of a photographer?

Look at his images.
Get references.

you can:

1) contact models he has worked with
2) ask him for references

but if you are already skeptical, doesn't that tell you something?

p.s. but whatever you do, don't post his name or identifying information in the forums

all good advice,if the red flags are there pay heed to them,but let's remember fear can  make you see things that are not there.Atleast give the poor guy a chance and check  references,credits,etc

If you're feeling sketchy even after research, I suggest telling him you can't make it due to personal reasons and move on. 

This is really the best for everyone. For example, I don't mind models cancelling well in advance, but no shows and last minute cancellations are the pits. So if there's a chance you'll cancel, do it early and soon than possibly ruining someone's day or weekend.

What models sometimes don't realize is that it takes time to schedule a shoot and it's much better to cancel / reschedule way in advance so the photog can do something about it.