When I sell via Craigs List, I treat the first contact as "Nothing will come of this." I will reply and then, in most cases, I delete the e-mail. If/when they follow up, I consider it a better lead that it might actually happen. Then I just about go overboard on planning when/where to meet. If they aren't serious, they won't bother keep replying. If they do, then I move to giving my phone number for a call/text. Once that happens, I contact them before I even leave to ensure they are still on the same schedule as I. If they don't respond, I don't leave.
CraigsList is nice because of no fees, but most times, eBay is just better. Auction ends, person pays, you ship. Done.