You may NOT promise/require a vouch for any item or service.
This means posting on your thread "giving vouch out if you train my account", or anything similar to that matter. This will break down on scammers getting unneeded "trust" for no reason.
Vouches should only be given out if the person has done a good service to you. Someone doing the training should not ask for a vouch, but wait for it to be given if it is deserved.
Breaking this rule may result in an infraction.