If I were you I wouldn't do any negotiating without being there in person. This is even more true when you haven't even seen the bike in person, I know this is your second time seeing this particular bike.
When I sell a bike on craigslist and they say will you take "$X" for the bike I just say I don't negotiate in person and they need to come look at it. Many times, they don't even show up. The reason is, why would someone make an offer without seeing the bike? It makes no sense and I think it is right to basically dismiss them as not being very serious. When they show up with a trailer or a truck. Then they are serious.
People that do this seem to be just after a "deal." They just want to talk someone down or walk away knowing that they wanted X dollars and they paid Y dollars. No offense intended at all, but you did negotiate a price for the other bike and then walked away. Think of how you would feel if you got there and he added a couple hundred to what you agreed upon?