1 - Forum administrators are not the sales police. From long experience on the board we can tell you about SOME of the involved parties but we don't keep records on the subject(s).
2 - Sellers decide what they want to sell, buyers what they want to buy. If you make a commitment to buy, pay up. If you get the money, send the item (IAW applicable law and regulation).
3 - Sellers are responsible for deciding to whom and under what conditions they will make a sale. Likewise buyers decide from whom and under what conditions they will make a purchase. If a particular buyer or seller doesn't like, for whatever reason, the other party's conditions, there is no obligation to complete the transaction until it begins through the transfer of money or property. Fraud is covered by law and if there is a fraud the parties involved have to pursue that.
4 - There are some general ethical rules in conducting transactions on or off line.
- If you offer something for sale you should respond to interested parties.
- An inquiry about a for sale item does NOT equal a commitment to purchase/trade.
- A response to an inquiry does NOT equal a commitment to sell/trade.
- Commitments typically include the parameters of the transaction such as "I will buy your gadget for $X and my old XXX," for a purchase offer and "I will take $X and your old XXX for my gadget," as an acceptance of that offer.
- Counter offers are acceptable.
- Sellers can entertain other offers.
- If a possible buyer doesn't make a committed offer he's just made an inquiry and must wait until the seller decides how to proceed.
If there was an issue over who "got it", there are date and time stamps for that. Perhaps, 
