Basically as a consumer, you should expect to pay for any service you are either unwilling or unable to perform for yourself. Never expect it to be free.
That said, small businesses are all about the relationship. Mechanics are like anyone- they respond well to people who act like they care. A $9 six pack of decent beer will surely buy you several times that amount of goodwill labor when you need a quick job done. Many don't understand this simple idea.
Our simple rule is if you bought the bike from us, all minor tweaks are free as long as YOU own it. Not your buddy who buys your used stuff! Little things like pedal swaps and simple accessory installs are charged only when the parts didn't come from us. Nothing more quickly identifies you as a leech than to walk in with mail order pedals, computer, cages, etc, and expect everything to be dropped because you have a big event coming up and need us to just "toss 'em on there for you".
As for the bolt, being up front is everything. Our usual speech at this point is "if you want us to try and remove it, we are happy to attempt it, but due to the nature of the repair, we cannot guarantee success. Our normal labor rate for this type of job is $X and is charged for our time. We should have a pretty good idea in the first 15 minutes if it's gonna budge, and if it looks bad, we'll call you and you can decide how you want to proceed at that time."
I think that's only fair. But I will tell you I value people's time. I do all my own repair work on my car but sometimes I run into a difficult diagnosis. I could take it to a shop and pretend I was going to let them do the work and get my diagnoses for free, but instead I find a mechanic I trust and offer him $20 to drive my car. I get an open honest appraisal and happily pay because it has saved me lots of money in the past. And, I'm not viewed as a bottom feeding leech, but as someone who values these people and their time/knowledge.
Just treat your mechanic like you'd want to be treated and the rest usually takes care of itself......