normally "refurbs" are just that.. something that was returned, sent back to manufacturer, tested or repaired, then placed back in the retail channel for sale.
that newegg doesn't themselves test it does not mean they are "simply customer returns being re-sold". i suppose it's possible, however newegg has been such a good "store"and have in my exp. always given above avg. customer service, i would tend to be optimistic and think they actually ARE refurbs, as they are represented to be, unless someone can prove otherwise.
as far as the results of purchasing refurbs, i've bought 2 "refurb" video cards from them, both came in retail boxes with all accessories, and both have performed flawlessly.
also know someone who has bought sever motherboards from them, and all have worked fine, and all except 1 (out of like 4 or 5) came in retail box with accompanying hardware.
as for returns, i did order a refurb which arrived as something other than what i had ordered, and newegg waived the 15% restocking fee and rma'd it w/o a hassle.