A lot of people will save a certain item to show to a fellow collector or friend and give them first chance at buying it. Often at a reduced price. This happens at shows or in person or by email. If I were to list an item for sale to the general group on old Gas, it would be sold to the first person that says "I will take it". There are countless "tire kickers" in the world. Sending a PM with a question without a commitment to buy in my opinion is only that, a question with no commitment. I am after a sale, not a question. The first guy that PMs with a question may or may not later commit to the sale, maybe after days or weeks. If you want it step up and say you will take it. Or even make it conditional, like "I will take it if it is porcelain, or if it is double sided, or if you will take $$ for it"
I lost out on the Sinclair aircraft sign listed on Old Gas a few weeks ago. I sent a PM, not the first, and I also was the first to post for all to see that I will take it. I did not get it, thats life. In the end, a person can sell their property to whoever they want but I think a person should sell it to the first person that steps up to the plate