... if I could not figure out the problem on the spot I would tell the customer that I would have to see if I could find a service manual for there appliance and stop back. Even if there was no service manual to be found it bought me some time to do a little research.
That was before I had internet access 24/7.
That was a staple for me when I was starting. I was really flying by the seat of my pants back then. Sometimes, I'd have to use that excuse just so I could figure out how to get the darn thing open!!
Thank God for the internet!
Other than that, I tell 'em I have to get the part, or, if I'm not positive which part
, I tell them what I think, then we typically start out with the cheapest fix.
I know it is pretty rash to start your repair business w/out much experience, but it gets you experience quick! I have had to eat some parts, and many hours, but I have not yet had a complaint from any of my customers.
Just reading these forums in your spare time gets you "experience."
In my area, I'm the only guy, so even if they'd call Sears, I'd still be back with them, receive the ordered part, and get it fixed, before they might get the appointment otherwise.