Joe, I'd like to see your complete list of customer #'s...
The problem that I see, you lack confidence in your ability as a sign guy and you may be "cutting your teeth" on a new customer.
What you really need to do is examine the way that you conduct business. This is what I learned from working at an ISO 9000 company, and I do what I learned there, at least as far as dealing with customers.
1. Meet with the customer and find out what they are wanting. Take a digital camera, and a color chart with you, as well as anything you would need for them to make a decision as far as options they want. Make sure to take a tape measure so you know exactly what your covering. Tell the customer that you will e-mail them a price on company quote.
2. When you get back from the customers location, sit down and figure out what your going to use, then make a quote sheet, and get it e-mailed to them. That way when they get it, they know you keep your word. It also gives them an idea of what they are getting / paying. (I do it the same day, or worst case, next day. Never more than that.) Plus you can put the terms of the job. (ie 1/2 down, 1/2 paid when the job is complete.)
3. Once they approve the cost, and cut you a check, then sit down create the artwork. Spell out the colors used (taht they picked). Put the artwork on the digital photo that you took. Once you have a signture on the sheet in your hands, that they approve the artwork, then you cut it, and install it. If you cut an extra set (for your own use, say on location in case something goes sideways when installing, never give it to the customer. That means in their eyes, the material is cheap enough to give it away.)
4. Install the materail exactly as in the drawings. If it is within 1/8" from drawing, your fine.
5. Pick up your payment check.
If there is a problem, ie, they don't like it, "I'm sorry, but it is exactly what you signed off on, with the colors you picked. Tell me what is wrong with it, and I'll try to fix it, for $xxx."
If you give the customer a chance to complain about something, some will take the opportunity. But if you remove the opportunity through customer approvals and signoffs, you won't have near as many. Plus it makes you more organized, and in the customers eyes, more professional.
I'm not on my computer in the shop, but there was a video posted up that you would do well to sit down and watch...Its called "f$%! you, pay me!"