Here is one more trick that I use.
I’ll go online and see what the client’s customers say about them. If you see a lot of negative press, that’s a sign their might be an issue getting paid. Always worth checking out to see.
Another valid point — you don’t want to tell the client he’s not trustworthy or you don’t want to take the job, bid it way high instead so you just get passed over. Avoid the conflict up front I’ve done this from time to time and it works with no hard fellings