Quoted from ccotenj:

yup. as soon as "offer a" gets pulled off the table and gets replaced by "offer b" (with "offer b" containing the threat, explicit or implicit, of "better take it at this price, or else someone else gets it) it is time to put away your wallet and walk...
i also believe it works the other way... if i as a seller start to feel like i'm being jerked around by a buyer ("i thought you said...", etc.), the item becomes "not for sale" to that person...