For me it depends where I am and what I'm doing when someone calls for a quote and I'm available to run over. If I'm at the office, I'll take my Durango R/T out after work, do up a quote, and head home after. If I'm at home and someone phones for a quote I like to do it as soon as I can in case I get busy with something. Then I'll take my '99 Taurus which is in optimal shape and no rust but has no markings on it.
I find that most people who call me, do so from the website, or from a current customer (referral), so they won't judge by what I show up there with just to write up a quote. The car gets twice the mileage my 5.9L V8 does so I prefer to take it for purely running errands.