Back when I had more money than brains (and that's going back a while . . . now I don't have an excess of either) I always (except for once) bought new. The exception was a pair of ARC VTM120s that I bought from the classified section in Stereophile (this was before the internet days). Those ARCs sounded fantastic, but man oh man they were unreliable!
Anyway, most recently I bought a factory refurb Maranzt SA10 from Music Direct and a preowned Cary SLP-05 from Cary Direct, and so far I am extremely pleased with both. The savings on each of those units was way significant. So significant that I would not have bought either for MSRP. I did have reservations, but as I typed, I am so far happy with both. The fact that they both came from dealers who should be reliable played a part in my decision making.
As far as the power cable example you mentioned--I'd jump all over the open box for $49 savings if it was from a reliable dealer (so there wouldn't be counterfeit risk involved) like Music Direct. $49 is $49, and that would be $49 I could then justify applying to something else.