Drake, if you really want to sell your one and only guppy fry, you really should wait until it's at least a couple of months old. Make sure it's going to be healthy and give it a chance to color up. Plus you would be better off just giving it away to someone local, as guppies are pretty cheap in the first place.
Plus, any buy/trade/sell posts should really go in the buy/trade/sell section of the forum.