Call me nuts, I just decided that I may takes him on his offer.

So I am pretty much a newbie in Bitcoin world, and decided that I'll be mining as my first step.
The seller mentioned he used his units for 1 month is there anyway to verify this? 
Also, typically if no overclocking is involoved at all, how long could I expect that a single unit of S5 would last?
Any help is appreciated.
