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My point is, that if someone has a reputation of accurately outing scammers then the scammer will not bother to ask for proof because he knows it can be provided. As what happened in this case, if proof is requested then it can be provided (it was quickly provided when asked for by the OP).
Also not all deals are done openly via threads. It is not uncommon for a deal to be done entirely via PM when one person sees a post indicating that they have something for sale/want to buy something (for example person B posting on person A's thread offering to buy a widget, then person C can PM person B to try to work out a deal if A and B cannot reach a deal.
I think we just have to agree to disagree here. I value your input because it is well researched not because it comes from a certain account. Maybe I am the minority here that does not make the standards less important.
If it is like you say that building a reputation to leave an accurate rating is enough than it is exactly like the long con with trades. If any dispute will just be seen as a scammer causing drama and no evidence is requested or vetted a position on DT can easily be exploited.