Likely a neutral rating if he (reasonably) put you under the impression that he was intending on purchasing. If his flaking (reasonably) prevented you from making a sale to other people, then that would be the option to choose. WWJD? He'd leave neutral feedback.
Of course, this is assuming that you're not one of those people who, when asked a simple question on the item, goes, "OMG UR BUYING U BUY U BUY!!!"
God, I hope not.
Age Verifier - Lower Vancouver Island
Brotherhood of Nod - Nod Prime || Vancouver Island Airsoft League - President