Let's look at things from the 'big picture.'
Contact with potential customers is the only way to let them know what you have to offer, and it's reasonable for them to want to know just what sort of money is involved. I can't count the various jobs I've had that were the result of several casual conversations, over many months. I mean ... what teen hasn't gone into a car dealership and drooled over some car he'll likely never be able to buy?
Unfortunately, I also have the 'other' memories: memories of folks who had no intention of getting anything done ("home inspection"), folks who were only interested in ratcheting the price down (including their kid as your competition), folks who were looking for 'instructions' before they DIY'd it, etc. I'm still PO'd at a supposedly 'loyal' customer who used me to plan the job, gutted the plan, then farmed it out to someone else.
The fact is, you need to be making money. There is NO 'free' time in your life. If you don't make it this hour, you need to make twice as much next hour. It's also a fact that you often won't be able to give an accurate opinion without first spending considerable time and effort scoping things out.
I recently saw an ad in Craigslist, where a guy wanted an electrician to troubleshoot and fix a circuit on a 'contingency' basis. Anyone else see a problem with that approach? OK, the guy wants things fixed ... but he wants an absolute guarantee, sight unseen, with you taking all the risk. Well, I want a night in Paris- but that's not likely either.
So it all comes down to: who's asking? What's your liklihood of getting the work? Just what's involved in making the estimate? If nothing else, a 'token' fee can help weed out the casual and unscrupulous. There's some merit to the argument that only the 'bad' contractors are available on short notice, and have lots of 'free' time.