If the proprietor was aware of it and didn’t object, probably not, because the tender of payment is an offer on the negotiated terms and its acceptance is…acceptance.
I would say it's pretty clear that buyer and seller in a yard sale are intending to create legal relations - viz. exchange goods for cash - this isn't one of those weird areas like family agreements or pacts between friends.
If, at the point the buyer put the dollar on the table, the seller suddenly changed their mind and said "no, it's not for sale actually", would a reasonable bystander actually think that the sale had been agreed? I would say yes.
BTW if you think this one is bad, check out the fun and games trying to rationalize offer and acceptance in the Amazon stores without checkouts: https://www.oscola.org/post/amazon-fresh-offer-and-acceptanc...
True, but manifest intent to form a binding contract on the part of both parties is.
> If you’re holding a yard sale, and I point at some knickknack and ask “how much for that?”, and you say “it’s a dollar” and I say “that’s a deal”, that’s a contract.
Probably not; contract law would probably view that as a negotiation where only you manifested an intent to form a binding contract, so unless there was some positive acknowledgement of your “that’s a deal”, no contract would be formed.
I mean, I’m pretty sure that a near identical scenario to that was the one the of textbook demonstrations of the absence of that contract element in my Contracts class.