I think I gave you advice like this before. Here is what works for me. After the customer tells me about their problem, I say, "If you have a minute to go over a few things with me over the phone, there's a good chance we might be able to save you the $85 service call". This way, if you DO end up having to go out there, they will not be expecting it to be for free. You will also get "points" for trying to save them money and perhaps solve their problem even FASTER than the same day service you already provide.

My business is much simpler, so I know this won't work for you, but I also send out e-mails giving people tips on how to avoid an $85 service call. So, when they do decide they need me, there are no surprises. I'm sure it cuts down on my income a bit, but it's a great way to stay in touch with my customers and perhaps it leads to referrals from them.