[glassdude]

Have them sign a work authorization form BEFORE you start working on the windshield.
Below is a sample of what I use. You can use it too to cover your ass if a windshield cracks out during the repair. Change it as you see fit to reflect your company.
---------------

Repair Authorization

I authorize (insert your company name here) to attempt repair on the chip/crack on my vehicles windshield. I understand that the purpose of the repair service being performed is to prevent further cracking of the windshield, and that upon completion of the repair, the damage may still be slightly visible. I understand that the damage is a week spot and I agree not to hold (insert your company name here) liable should the windshield crack out while attempting this repair and that there will be no charge for the repair should that happen. Since your windshield is already damaged and we are attempting to repair the damage from spreading further, (insert your company name here) is not responsible for the replacement cost of a new windshield.

All work is warranted for as long as you own your vehicle.

Customers signature:_______________________________
---------

Have this printed on two part carbonless paper from your local printer or from a service on the internet.

Good luck and have fun.
-Jeff