Just got an iMac and it was dead on arrival. Spent 2 hours on phone with tech support to no avail. Then another few hours negotiating a deal on a new one. Saleman told me that I had to expect something like what happened since it was refurbished and not new.
What a royal waste of time...
The exact same thing can happen with a brand new iMac, or with any other brand new computer. Some percentage of computers sold will arrive dead; that's just a fact. Any statistic that I ever read indicated that Macs were better than your average PC, but with 4 million sold each quarter, the number of dead computers is still a six digit number.
The sales person is talking out of his or her arse. And if he or she was an Apple employee then you should have asked to talk to their manager.