I had an Apple Service center replace the top half of my MacBook pro 15" due to a crack in the screen. Ever since then I've had horrendous wifi reception. When I talked to them they said I'd need to drop it off for 3-5 days for "diagnosis". I was 99% sure they hadn't reconnected the Wifi antenna correctly, but still, they wouldn't just open it up and look at it (even with the Applecare #)
Took out the screws, found the loose antenna connection, connected it, and closed it back up. Instant happiness. Took 10 minutes tops.
Used the Pentalobe driver to open the back case, and used the precision tweezers to grab the insanely small connector.
If you have a modicum of mechanical ability, many common problems can be fixed. Granted, this could have been a more serious problem, but I didn't lose 3 days without my main work machine in order to tell me something that I already knew (WiFi reception was poor, most likely due to antenna not being connected).