I, too, deal with the same guidelines that you do. I have also had the same experience you have had with items being sold out from under you. I called out one of the sellers because my time stamp in his ad was hours before the guy that he sold to. His response was that he mixed up the PM's and responded/sold to the second guy by mistake. He could have made it right, but chose not to. I have a few people on a list that I won't deal with here. It's your best option with things like this.
I've sold quite a few things here and never had an issue, I've only bought one thing here I think (tipi stove combo) and that guy even offered to hang on to it for me a little while so I could sell a spotter to cover it. I'd say your experience is not the norm 'round here...
Don't let the few jerks discourage you this place is full of stand up outdoorsmen and women...