A bank line of credit is fine as a last resort. Show up with your contract or purchase orders to the pledged job. That way, the banker sees proof that you will promptly pay off the note when that job is paid. Charge enough to start with. I want mine, now.
Good communication is the key.
The contract is the best form of communication, because it can always be referred to at a later date, if there is some question about the terms. Don't be afraid to ask why you're not being paid, and try to work with your customer to stick with the terms. The biggest problem in dealing with GCs is that you're never talking to the person who is actually pulling the trigger. Get to them, and you'll usually find your money. E-mail us and let us know what you think.