It isn't a great idea IMHO to buy a cell phone on ebay, especially a BB. There are many who have done fine, and probably just as many who have had problems.
The issues have been hashed over and rehashed over on here many times. The two biggest issues being IT policies left on the device and BIS not being closed so the buyer can't seyt up email.
And ever so often you see someone getting a great deal only to find out it was a lost or stolen device.