Growing up, there was a quote from John Ruskin that was posted at the local ice cream parlor. It read "There is nothing that cannot be done more cheaply by someone, and those who consider price alone are that man's lawful prey."
Someone asks you to quote a job, they're giving you an opportunity to set yourself apart from the pack. There's your chance to outline the OTHER reasons you should get the job, apart from just the price. It's NEVER in your interests to let your work become a commodity.
Sure, some folks just don't get it. I once had a customer get upset because I asked about the bathroom mirror plans; they actually went so far as to deliberately give me the 'wrong' answer just to show how 'smart' they were. They also got to pay to have the receptacle relocated. I asked- they lied - they paid ... all because they felt that I did not have the 'need to know' where the mirror would be hung.
I've also had multiple times when folks specified lights in locations that would become completely inaccessible after the job was done. Makes it kind of hard to change a bulb later.
What I am getting at is that the customer needs to know just what sort of contractor you are - and weigh the bids accordingly. Sure, there's a lot of 'guessing' involved. We call it 'professional judgement.' We've all had the joy of being given a blank floor plan and being told to 'make it work.' We've also been able to learn as time reveals all of our wisdom (or foolishness).
That experience we count on to let us spot the unusual in a plan, and examine that part more closely.
Sure, sometimes we lose. I lost a bid for a hair/nail salon because I bis a hair/nail salon, while the other guy was allowed to bid a simple, non-specific division of a commercial rental space. Where I had a dozen circuits, he had four receptacles. Where I had task lighting, he simply left the ceiling grid 'as is.' I still a bit upset at the way the CUSStomer misled me, but he has to live with the results. I expect he'll have some problems with his future tenant. I'm probably better off without that particular tar baby.
There's your choice, in a nutshell. Do you quote 'as drawn,' or as he 'really wants.' Either way, you need to make clear just how much uncertainty you're willing to accept the risk for. If you plan to quote strictly on what is drawn on the "E sheets," you must specify that. Let the customer sort through the declarations as well as the prices; that's HIS job.
It's not JUST the 'bottom line.' It's a CONTRACT. Remember that any uncertainty in a contract is understood against the guy who wrote it. That means HE pays for his lack of clarity. You wouldn't hand over a blank check to a stranger ... why would you accept a blanket acceptance of responsibility?