Most people wont buy reloads since they don't know exactly what went into them, or if they are safe or not. Noone want's a blown up gun.
That said, it's illegal to manufacture and sell reloads. On the flip side, if someone reloads 500 rounds for their firearm, shoots 450 of them, and then sells it, I have heard of people selling the remaining 50 rounds as "for components only".
It is my understanding that you can sell them, but not with the intent to do it as a business, or for any sustained period. If you have an amount of ammo for a caliber you no longer shoot, selling it simply to liquidate it, is legal from what I understand. I'm not a lawyer, but from what I've read it seems to be ok, as long as its not with the intent to get into the business of selling reloads.