Well, to your scenario, ya win some, ya lose some, but you can create a way to have less of it. It's called customer education.
Regardless if a customer calls or e-mails, make sure you explain a few thing to them before giving them a price.
What I usually do is, figure out a Plain Jane price, a middle-of-the-road set up and then a really nice set up... with a little room to go up from there, if need be. Called a 'three tier' method.
I explain how they will all do the job, with some being better looking and longer lasting than than others. There is a way for any shop US-A to get almost all of your quotes. Be able to roll with the punches. Not each and every truck,
sign or banner need to be home-runs. Singles work, triples and even walks, but a strike-out will happen usually if the customer doesn't know any better and that's what you are complaining about and you did nothing to elevate them to your level. You left them in the dust to be picked up by a...... hack. They'll take anything at any price. So, ask yourself.... are you a hack or a professional
sign person ??