Sounds like a noob that built what sounded really cool.
The motherboard is overkill, the "850w" psu is probably a cheapo, got a Kingston junk ssd drive, and is actually trying to say wifi is a premium over a solid wired connection.
This one is a toss up, it has some really nice parts in it (minus the psu and ssd drive), but looks like it was not built by a guy that knew what he was doing.
This could be a great find where he just did not get the water cooler attached right or his overclock is such crap that it is running bellow factory performance, or it could be that he already damaged the parts. Could also be that all the unstableness is caused by his cheapo power supply.
Might be good to just get the computer, replace the PSU...