This is in the FAQ on the Benches Policy.
1) New members will be required to send first on all trades and assigned the New Member avatar. If two new members are trading with each other, there will be no such restriction.
2) New members are not allowed to sell until they reach 20 Bench points or are upgraded to regular members.
3) Once a new member has completed their end of at least 20 trades with at least 20 different members, their status will be reviewed. If they have completed their end of the trades without incidents including a 5.0 trader overall rating, they will be promoted to a regular member and be allowed to select their own avatar.