My air-con stopped working, so we took it to Greshams to get it re-gassed. He said he thought there may have been a leak, but gave us the car back in case there wasn't. The re-gas didnt work so there must have been a leak. We took it back for them to have a look at (for free) and he then thought it was the evaporater and was going to cost upwards of $600. We dropped it off to get fixed, and a couple of hours later we got a phone call saying the problem wasnt what they thought it was and only ended up costing us $260.
Very happy with their honesty and thourough-ness!