An explanation would be that your asking price was ridiculously underpriced. The man saw that and thought you are obviously clueless, maybe he can make you go even lower. After you raised the price he abandoned that strategy and just bought it.
the few times I've sold things on craigslist or whatever (I'm usually a buyer) as soon as the person has accepted my offer I'm instantly concerned that I way underpriced it and want to reneg lol.
