My Idea:

A list somewhere that shows all:

Scammer Tagged
Gold Locked
Banned
Multi-Accounts (Accused/Proven)
Max Warn % at any point for a given user (optional, would take a lot more effort to include, as it involves cataloging all users)
It should include all users that have been previously locked/scammer tagged.

This could prevent a large number of scams if people could learn just this little bit more about the person they are trading with.

I understand this would take a lot of time and effort to catalog all the Jsp users and pretty much their entire history on Jsp, but I believe
this could be a major asset in the long run and would lessen the Mediator/Trusted workload immensely. (I hate those 30minute+ waits for Meds)

Anyways, this is my first site suggestion and I hope it goes well.

If this has already been suggested, I apologize.

wouldn't be hard
would just be a simple sql query
and I don't think this would work at all to prevent scams, most people that scam are on new, undiscovered multi accounts
if you think about it none of the criteria you list will aid in the detection of a possible scammer

yea if someone has a scammer tag why would you need to check a list lol
voted no cause it seems useless

nope