It would be nice to have an interface where collectors could buy/sell/trade directly with one another. The "For Sale" section of this forum could be that type of venue, but the problem with it (as is the problem with all interfaces of this type) is that there is very little transactional security. Either the seller has to ship first or the buyer has to pay first, which opens somebody up to getting screwed over either way. This reality has led the owners of this forum to pin posts in the Sell sections for the purpose of avoiding liability. In short, they say, "Here is a Buy/Sell forum for you to use, but if you use it then you are an idiot!". There are, of course, interfaces where you have some security in the transaction, but then you are dealing with people that have decided to make a living by skimming profits from collectables transactions. In this case, these middle-men take the form of auction sites and/or coin dealers. The downside of this is that, for the middle man to make a profit, the seller, buyer, or both must lose in some way. Long story short, we can't have nice things because people suck. Unfortunately, this general rule applies to pretty much every social system
Not everyone sucks, but I get your gist. However, as an example, Frank Robinson runs a auction a few times per year. When I have won a piece, he generally sends it before I even have a chance to pay. There for a while, I was selling off a few coins from my collection through an auction I ran through PM here on CT. I tried to be like Frank and send the coins once there was a winner even before I got paid. I was never snookered. But, a few bad apples can spoil a barrel as they say.
I tried to dramatize my point by over-generalizing to be sure. But, as you pointed out above, every person sucking isn't required to ruin things for all. Any system that can be exploited for personal gain will be taken advantage of by some small portion of the population that is lacking in ethics/morality/civility/principles. Unfortunately, that renders useless the system as a whole. I've won coins in FR auctions a few times and did notice this to be the case, he sent them immediately even on my first purchase if I remember correctly. However, Frank has also posted a very long list of people on his website that never paid for the coins that he sent. I try not to let myself get too cynical, but the truth of the matter is that trusting people by default will cost you in the end.
As a member who usually likes only specific groups of ancient coins, such as Owls, Flying horses, Gargoyles, etc. I need to deal with someone who I can trust and I recommend JAZ on Vcoins who ran auctions on ancients on Cointalk with personal messenger postings. https://www.vcoins.com/en/stores/jaz_numismatics-311/ancient-coins/Default.aspx? Jim