I have to disagree on the "buy by price" theory regarding CPUs. We're talking about the most important part of your computer and I'm often shocked when I see people obsessing over something as meaningless as a shiny spot on a keyboard, which is really of no importance at all with the function of the computer, then assigning the same value to a low milage mint cpu as you would to one pulled form a laptop that is dead, smashed, or even fried in electrical fire, or in the case of a high end cpu, one that has likely been overclocked and overheated dozens if not hundreds of times.
I've had opportunities to sort through corporate laptops to pick out the best of the best before anyone got to them, usually looking for units to source for rare system boards and other parts, but if you've seen what I have, you'd be very careful buying a cpu from someone you don't trust. When a shipment of hundreds of laptops comes in, the ones that I don't select for myself are auctioned to brokers who then list the laptops for sale on various websites including ebay and others. With every "lot" there are always a number of units that even the cheapest of the brokers won't touch. These are loaded onto pallets and shipped to Asia where part stripping factories, employing child labor strip out all the parts, usually untested and sell them. Most of your low priced CPUs come from these, some of which are computers that have been in electrical fires, smashed so badly that they're in many pieces, and some are just dead, for various reasons.
Keep in mind that the people who sell these parts are motivated only by profit. They don't waste time testing them, they leave that upto the buyer. When one is bad, they offer a replacement and most buyers are understanding and are only concerned with getting a refund or replacement and usually leave favorable feedback even if they get a bad one the first time... but it's far cheaper to ship a couple extra units then to do testing of each component beforehand.
Granted that it's very possible to pull a cpu from one of these and have it work... even from a unit that was in an electrical fire, but if I was buying a CPU and had a choice of an unknown CPU for $50, or one pulled from a mint condition unit that is fully functioning for $100, I'd choose the latter... and the really ironic part is the price difference is rarely that vast.
My opinion is you use at least the same care when buying a cpu as buying a keyboard or display... no one here would buy a display without asking questions about it's condition. If you have a seller you trust that has personally tested a computer before pulling a chip, then I'd assign a premium value to that chip as compared to an unknown chip from an unknown seller. I often purchase corporate laptops to fill orders for rare system boards. In testing, these machines are run for several days to make sure the boards are good, then in most cases things like the CPU's are sold later, or used in custom builds. I would never buy the cheapest chips I could find. Even if they do work, I'd still not trust them to perform upto spec. These chips are so complex and some develop things like hotspots within them, and some develop thermal issues that aren't easy to demonstrate, but could cause problems that are very difficult to track down. It's also possible you're buying someone else problem. High end chips that have been extensively overclocked can develop thermal problems, then get dumped on ebay when the person upgrades to a better model.
Sorry for being "long winded", and I'll just sum it up by saying... be careful. Certain parts are ok to buy by price alone, but definitely not a system board or a CPU.
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