In some ways it reminds me of the old Army Air Corps radio repair where they had a simple rule: "Kick it. If it works, replace it; if it doesn't work, replace it." I've seen how HP and Dell tend to troubleshoot their PCs and I've had to cycle a single machine back for multiple repairs on symptoms that were pretty obvious to me. An intermittent problem is highly unlikely to be software related which narrows the problem to some hardware component, whether it be drives, power supply or mo-bo. You, yourself mention things like loose heat sinks, cold solder joints and other faults that the proper questions asked to the user can expose. Apple, unlike these others, then aims the refurb in the proper direction to resolve the issue, up to and including replacing an entire mo-bo on the first try. I've also seen Apple put a device on an extended testing cycle if the problem is intermittent to try and isolate the exact symptom.
I've owned three different Apple computer refurbs over the years and have never had one fail on me--never. I couldn't say the same for any other brand. In every case I donated the computer to someone who needed it, in one case to a mother who couldn't afford one for her child and in other cases to a church and school for repurposing. Of course, having only one Mac fail out of the box out of over 20 different models over the last 20 years (I currently have 5 serving different purposes around the house) which was replaced with a cross-shipped twin and another that had a power supply die after 5 years as a 'mobile' computer (Weekly trips to a second home before I bought a laptop), I can only claim that no other computer brand or model that I've built myself has demonstrated that kind of longevity and reliability.
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