Quote or estimate repair jobs

I am looking for advice on how to quote or estimate customer repair jobs. I know on certain repairs you can hard quote, but some troubleshooting jobs just cant be quoted the same way, so do you just estimate a ballpark number? How do you go about quoting? What if it looks as if the troubleshooting may take a while, how do you sell that to the customer?? Is there a industry standard? I am not able to find anything as far as labor repair hours.
thanks in advance for any help!

Quote or estimate repair jobs