Vouches are used in UKScenario, a new member can buy but cannot sell without a vouch from an 'established' member. The vouch shoudl be from someone who actualy knows the new member so that they are providing a point of contact / guarantor of the new member.
This takes a lot of effort by the forum mods reminding prospective sellers of the rules. Sometimes they give a gentle reminder and allow some time for the rules to be complied with, e.g. to let the vouch get posted, and to enforce other rules such as a 'proof' photo with the username & date. If the rules are not complied with in a reasonable time, or the new member does not seem to have any intent to read the rules and comply then the sales post is edited out with details of the rules that need to be complied with.