I've recently purchased what I consider to be a second hand mobile from a well-respected vendor - it was advertised as refurbished, mint condition, but in my opinion if it was actually refurbished it would've been like new cosmetically, as well as being 100% guaranteed to be defect free.
What I got was a slightly less than perfect (cosmetically) second-hand phone, with minor scratches etc on it, a bit of dirt and a 1 year back-to-base warranty.
I'm not at all convinced that it's been refurbed at all...I'd say it's simply second hand and being on-sold.
I'm OK with that as it's under warranty and I can live with that for a less-than-new price, but my question remains...what constitutes refurbishment?