I really just want to back up what Rob S is saying here and add my 2 cents along the way.

I've repaired thousands of electronic/electrical items and I have to say that the worst repairs to undertake are generally the ones when you're not the first person on the job. That's not even to say that the first repairer made a mess of things to be honest, although, sadly, it's more often than not the case

To a knowledgeable engineer, electronic components and their fault mechanisms can be simplistic in nature and the remedial course of action, while not necessarily quick or easy to perform, is quite apparent and well understood.

If you add to that mix the random unknown elements of a previous engineer, no matter how good or (usually) how bad they are, it can can transition the work into the realms of "uneconomical" all too readily.

As an example of how this can happen on both levels, while waiting to be served at trade counters, I often witnessed Johnny coming in and asking for a fuse and a transistor for his TV - he'd tested them and they'd both blown. Quite often I'd know the set/chassis and its symptoms and I'd know that the transformer (and/or other components) was a goner too. Because the cause still existed I also knew that if Johnny just replaced the fuse and transistor they'd both blow (instantly) and almost certainly do a whole lot more damage further up the chain than had been done already.

Imagine receiving a repair like this; it should have required a thingamabob and a doobry replacing/checking. It now needs the fromitz board, flux capacitor and the 10ohm bedistor changing too, and that's after the extra time (money) taken to diagnose it, not good.

When I used to do repairs I'd aim to spend 15-20 minutes at most on my pre-estimate diagnosis, this included writing up a brief estimate with approximate component costs. Sometimes I could confidently do this without even opening the casing on whatever it was and at other times I'd end up spending 5+ hours diagnosing the damn thing - time lost with no income but sometimes your work ethic meant that you couldn't just walk away and say "sod it, not worth it" and condemn the unit to the scrapheap. It just happens like that, it gets personal -- but not the kind of personal where the customer is hassling you every 10 minutes, those units tend to be B.E.R. (Pushy / obnoxious customers please take note!)

I could be wrong here but I bet I'm not; Rob S probably can't bear to see an empeg that originally needed (say) 1 hour's work, sat there in front of him subsequently needing 5+ hours T.L.C. to cobble PCB tracks together in order to resurrect it etc. The owner won't want to pay for all that which in turn means that Rob doesn't get paid and everybody loses. Not to mention that that's another empeg out of circulation.

When I worked in electronic repair (I don't any more), I came to realise that EVERYONE (alsolutely no exceptions here) had a friend who is either an electronics or a computer expert - why people ever bothered coming to me with repair work completely baffled me

Be choosy who you entrust your EOL empeg repairs to!