you can read back through the last 50 posts of a member to determine if they are worthless or not yourself.
members with less than 50 can always ask a moderator for permission. this has been done countless times. yes, at times well respected but infrequent posting members do sell items and they still have been able to do so. it just requires vetting by a moderator.
it's not perfect, i get it. it's what we have and what has served us well for a very long time. were always open to suggestions however