Seems like you're sore over missing a couple deals. Thats just part of the knife buying game unfortunately. At least here you have a better chance at scoring a deal than on reddit. I saw the threads and sellers you reference, the one guy seems a little nitpicky on who he sells to, but it really is up to the seller who he decides to sell to.
To be clear, the main reason you buy Gold (other than supporting the awesome community) is so that you can sell and you can ask about value on pieces you own. You aren't buying yourself a purchasing advantage, though some folks like one you dealt with prefer to use PMs which non-paying members can't use.
I'd also recommend looking at other threads for general sales etiquette. Posting "Still available?" is not necessarily going to snag you the knife, most sellers want an "I'll take this" which I would post even if you're not sure it's available. Welcome to BF.