I rather buying a used pair of headphones from friends, buying refurbs its a matter of luck.
Probably better going with "B" stock.
Edited by thecourier - 10/25/12 at 10:58am
I would personally only buy 2nd hand through head-fi or B-stock on some of the reputable headphone sites.
That said, if they were refurbished by Sennheiser, I would reason that perhaps it isn't as large a risk.