Can the htc evo be unflashed back into sprint?

[djzombeatz89]

i bought an htc evo from some guy at craigslist yesterday and the esn number was clean and activatable to sprint so i activated it but me and the agents had such a hard time because the phone would not activate. they tried to get me to dial some pound numbers to bring up the programming menus but would never pull up also they tried the hands free activation and never worked. either so turned out that i was told that the phone was flashed to cricket. according to sprint. they said not even the sprint store peoplel could unflash the phone. wanted to find out if any body knows how to unflash this phone becuase i really want to use it on my sprint service. and not with cricket. also how could i know if the phone really is flashed?