IMO,
you have to think about electronic postings he same as the tried and true "bulletin board notice" where someone leaves a note with a number. Then the communications take place outside of the governorship of SS. Which is what you want. There are a couple points to reinforce this..
1) if SS is facilitating communications where someone rips people off, sells stolen gear, absconds with payment or other nefarious law breaking, they could be party to a lawsuit. Regardless if they are "guilty" it will drain resources to defend it.
2) The "contract" to sell and negotiation of it should be private, this is an agreement between two people not for SS and certainly not the public to know about.
3) if someone "undercuts", offers a lower price, or "attempts" to snipe someones "deal" who exactly is to blame? The person who tried to get in on the deal like everyone else, or the seller who didn't honor the "first come, first served" unwritten legal "contract". Either way it isn't SS responsibility to "police" the selling and buying behaviors of its members.
Bottom line here is this.. "what is the purpose of SS?" to allow people who enjoy Military "stuff" to exchange resources.. either knowledge, goods or services.. period. anything beyond that drains SS resources away from keeping its primary mission alive.
People have a problem where they try to use "popular" mechanisms to reinforce personal or adjunct beliefs or ideas on others, even when enforcing those will reduce the primary mission of the "popular mechanism". if your good at some things, it doesn't make it ok for you to try and enforce everything else.
Stay focused on your core mission, leave the rest for someone else.
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