My feeling is that If I say "I'll take it" and we've worked out the details where, when, and you back out for a better offer I'll be reporting negative feedback and going to the Mods for a decision on your banning. I'm a little surprised at this attitude here that after we have an agreement that you can just take a better offer. I guess no one has read #4 in the sticky in the BST thread. I've sold a few things here I know I could have gotten more for but once we've made the deal you got it.
4. If you agree to a price, time and location, your word is your bond. Almost without exception, people acting in good faith are able to reach accommodation and achieve a positive transaction even if someone's car breaks down. HOWEVER - staff will not hesitate to take punitive measures (including temporary or permanent site ban) for not honoring your word. If you don't know what it means to keep your word, do not post in the classifieds.
I hope I didn't give this impression. But I certainly didn't mean to. I would never back out ONCE I HAVE ACCEPTED an offer.
Rather, what I meant was I would be kind of picky as to which offer I would accept. And the offer I choose might not have anything to do with the chronological order in which they were made.... which (I think) was OP's impression.
This all seems pretty open and shut. If an offer has been ACCEPTED by a seller, that seller is duty bound to go through with it. But that seller is NOT duty bound to accept the first offer made, even if the offer meets the asking price. Time and logistics come into play here.
Here's where (in my view) it gets tricky. If the seller has a ton of details as to his/her terms in the ad, he is possibly getting into a grey area.
Here's the scenario.
"For sale. One slightly-used hand bazooka. Like new. Asking $1,750. Must show ID. FTF only at Lowe's parking lot in Greenville, NC on Tuesdays if it's not raining at precisely 3:17 p.m. You must drive a red car. You must have a beard. You must bring me a dozen glazed Krispy Kreme doughnuts."
If someone replies "I'll take it. I drive a red Corvette. I'll bring you two dozen doughnuts. My beard is glorious to behold. 3:15 is my favorite time of day."
Although technically the seller is still not legally bound to accept, I can see where a buyer might get pissed off a little.
But all of that was semantics and just for fun. Until an offer is ACCEPTED, you got nutn.
By the way, OP, how do you know you were the first offer anyway? Perhaps someone made an offer via PM without a public declaration.