GEEZ, that sucks big time! I've never met anyone like that, but I know they're out there.
Don't get bummed, just keep searching, they pop up quite often especially in the area you live. Next time don't make any offers over the phone, just ask about the bikes condition, and what they've done to it recently like any maintenance work, then get the address and go look at. Once you're there and you've studied the bike for a while and taken it for a test ride then make your offer, because now you're there and you're his exclusive potential buyer, if the seller doesn't come down far enough for you to consider buying it don't get into an emotional buying frenzy, just leave your name and phone number and tell him if he changes his mind to call you, then walk away. If they do accept an offer you agree on then make sure you then ask for any extra parts, bottle cages, seat bag, tools, etc, the original sale invoices and perhaps even the brochure he might have for the bike, A lot of these guys buy a bunch of bike gear for their new bike hobby and then give it up so they could have all that stuff and have no need for it anymore but they forgot to include it all.
About 60% of the time when you walk casually away (to give them a bit more time to think) from a deal they'll yell at you to come back before you get the car started if you didn't offer a ridiculous offer and the seller knows it's within reason, if they don't yell at you to take the deal about 10% of the time they will call you within a week after they got no other better offers. There are some sellers who simply don't care if they have to wait 6 months to see the bike, they want the maximum price and they feel if they wait long enough they'll get it, but others are in a hurry for cash and or clear out the space the bike is taking. So it's sort like gambling, the odds are in your favor but not by much. If you do walk away just keep looking, don't wait for the previous seller to call, and don't get into a hurry either or you won't get a good deal.