Unfortunately with manufacturers telling customers via the media that their products are so perfect they will never go wrong and with purchasers gullible enough to believe it, then we will always have customers like this! I try to set the customer expectations first, "no Sir, it probably isn't just a fuse" type of conversation. Money's tight and they want to spend as little as possible, I just tell them that I can't find a cheap fix to an expensive problem and I don't know what that problem is until I have looked! I usually say that I will investigate for 2 hours and then report back, as I think that in 1 hour you can only do the really basic tests, bearing in mind I get a lot of trade referrals and if it just a dirty air filter someone else would already have found it (means I rarely get the easy ones).
Shaun