If you had a price in mind, you should've stated it in your ad.
It was your choice to quote him your lowest price. I would've said $750 to his original question of price, and negotiated from there.
Now you just appear difficult to work with.
BTW, one of my peeves is people who don't/won't post an asking price. As a buyer, unless it's something I REALLY want, I refuse to price an item for a seller, and then buy it.
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My bikes: '81 Trek 957, '83 Trek 720, '85 Trek 500, '85 Trek 770, '81 Merckx, '85 Centurion Cinelli, '85 Raleigh Portage, '92 RB-2, '09 Bianchi