I don't think I'd ever buy one from an individual seller (eBay, Craigslist and the like), but if they were sold with a warranty from a trusted brand (eg, Verizon 'certifying' the refurb with a warranty), then I'd be ok with it. It's kinda like buying "BMW Certified".
Otherwise, I fear that "refurb" would mean polishing it up real nice on the outside, and the inside is still suspect.