I have been buying off of eBay for over 22 years.  I only buy from sellers with 99.8% or better good feedback.  And I do not buy the lowest priced item.  I just bought a Dell D630.  Low price was $55.  I bought a nice one at $105 from a seller who has great feedback.  No issues - the D630 was better than described.  I would NEVER buy from a seller with 96% good feedback.  Exceptions for me are if the item is one I have been looking for for a very long time and cost is $40 or less then I will take a chance.  Otherwise I keep waiting.
I've bought three 2-3 years old laptops, and techically they are like used not 2-3 years, but like 5-7 years.A year ago I've bought two 7480 laptops from 99+% positive sellers, one of the laptops was declared in the great condition, and it was okay except seller lied about the display resolution and display type. Another one was declared as excellect condition and it's actual technical condition was not good at all - mainboard that generates memory errors, high frequency noises when charging, near dead battery, some screws missed, but with a really nice keyboard, that better than in 2 others. A month ago I've bouht 7490 that was declaed in excellent condition from 96% positive seller. So.. what I've got - screen was replaced with fhd ips, but worse than original, not original but almost new battery, not original ssd but ok, not original memory but ok, and the issue with mainboard - high frequency noises when cpu frequency is above 3Ghz. Just one question - if I bought it new, would I got 90%+ chance that everything would be ok for at least 3 years? Sadly I have no idea what to buy new, because one of major things i like in 7480/7490 is keyboard, especially up/down/left/right/pgup/pgdown/home/end keys - but 7420 has completely different keyboard layout that i don't like.. so.. no ideas..  
Why is 2-3 years old used 7480/7490 laptops than can be bought on ebay are 
almost always in the fair technical condition ?