Well Billy - They should paint "No Electric" on the ground, and before they leave you should take a picture of it, hopefully with the locate guy in the picture. You can imagine how valuable that picture could be.
Even with good locates, you can still screw up, but there's no need to take the blame if it ain't your fault.
Someone said ten feet on each side of the locate. We always figured three feet, and I'm not sure it really isn't 18 inches each side of the paint that you're liable for.
The worst thing you can do is find a phone line and think it's the one they located. There's so many dead lines in the ground - you can think you're home free 'cause you found it, then next bite you cut the good one. If they see that you're making a genuine effort to protect their investment they'll usually go out of their way to be good to you. That all ends when you cut a fiber optic line. Second call to make then is to your insurance company.