Practical board repair how do you avoid rabbit holes?

[busyfone]

Time is money in the world of general phone repair(notice I'm talking general phone repair NOT data recovery) and in order to make a living, a working technician, needs to quickly identify phones with problems that are NOT cost effective to repair and reject them (the 'right way?' so as not to offend the customer)- particularly if the business model is a fixed repair price with no fix no charge policy. Could you share some strategies to identify when one is potentially going down a repair rabbit hole?
Boot looping issues are one thing that comes to mind for me..... I'm also thinking about the practicalities of diagnosing shorts in light of No visual clues, No available history, No heat....

[Jessa_the_Professa]

For Business: A phrase I use a lot is "We don't offer a solution for that problem" We only take in repairs that meet a standard--we already have a good idea where to look and how to find the problem and solve it quickly. Otherwise....see line 1.

For Research: With that said we ALSO take open-ended problems that may become tomorrow's signature problems as long as we get a sense that Problem X isn't unique. For example, the first "intermittent touch with flashing gray bars" would have been a big hell no. But the second or third time we hear the same description---we will devote an enormous amount of time to figuring out the problem.

For Hobby: I tell students that their number one job is "to protect the fun of board repair" I will sometimes take an interesting job with an interesting story or something weird as a hobby project that I work on off the clock for the love of board repair.