No one is perfect but you don't need to lie....

I agree I had a guy do that to me on Facebook. Then later on tried to trade the exact same part that he told me was already sold for something I had for sale. I guess he had forgot he lied to me. Basically what happend he priced his stuff to low and after a 100 ppl jumped on it in 2 mins he realized he messed up and then went to another group and tried to sell the same part for 5 times as much but didnt know the same ppl was in both groups saw thru his shadyness. The way I fell about it is like you said even if you have a deal unless payment is sent it's never to late to back out just be honest.
I had a guy one time locally I had a gun for sale and I was looking for a 8.8 rearend he told me that he had a buddy with one and asked what kind of trading I'd do. I said I would be willing to trade even if (big if) it was what I was looking for. He said give me a couple days and I will get back to you. I said ok. Well that night i found a rear end on fb for 100 bucks. The next morning I messaged the guy and being polite and honest ( I didnt ghost him or lie) told him hey man dont worry about the rearend I found one. He sent me a message back and sisd oh hell no a deal is a deal you cant back out now. I was like what? You haven't even found one yet at 10pm last night you said give me a couple days. This is like 7 am and your telling me you already went out and bought one give me a break. It's not like we had met and shook hands and made the swap. We had a 3 sentence message on fb that is not exactly set in stone. Lol