I'm impressed that you got a BB employee to sell you an Evo in the first place. Everytime I set foot in a BB store, all I get is, "You want the Iphone, you want the Iphone, you want the Iphone accessories with that Iphone..." It's freakin annoying!
Anyway, I feel for the OP here, I mean sure, Sprint can fix it up whether you get it at Best Buy, Radio Shack or Sprint stores. The question is, will Sprint step up to the plate and take care of a subscriber with issues or is this another dissatisfied customer that will continue the bleeding that the Evo was destined to stop.
First thing I would recommend is taking the Evo to your closest Sprint Repair Center. If they can't fix it, they won't care where you 'bought it' they will either give you a new one (or for some reason if there are already refurbs in the loop you might get one of those) but at least it will work and give you the experience that the Evo should deliver. The other thing to do would be to 'reflash' the ROM to the phone. It's possible that something did get corrupted and even the hard reset won't fix it. I know it sucks having to 'reset' the phone to out of the box, but you'll be doing that anyways with a trade in, so give it a shot.
If you don't have the stuff to reflash, a repair center will.
Good luck and thanks for joining me in the 'I hate BB's Customer Service' support group. I know that some BB Employees are great and some shoppers have wonderful experiences there, but frankly, my store and the associates there - well - suck...