There are a lot of phones advertised on ebay as "brand new" for Nextel.  Lots of these phones have had the housing changed and are, in fact, not new.  There is an easy way to tell:

From your Nextel phone, hit the keys in the following order:

1.  #
2.  * (star key)
3.  menu
4.  right arrow.

SIM card needs to be in your phone in order to do this.  Scroll down to "total usage."  If there is no number listed it's brand new.  If there is just a few numbers then it probably just had a few test calls.  Anything higher and the phone is a refurbished model.

There is nothing wrong with selling a refurbished phone.  In fact, because they have been thoroughly tested, they often work just as well if not better than a brand new phone.  But if a seller is going to list a phone as "brand new" sometimes it's best to just be honest.  There are a lot of savvy consumers out there who know the above and it just isn't worth the negative feedback.