Well, this board is one of the very last one who still keeps this business area 'hidden' for non members (check all the uk board for instance)...
Adding a minimum post won't really help (or this should be very high number) I'm afraid, you'll have plenty of 'I like this', or 'my favorite game is' or 'I'm x years old' topics in no time for the newcomer wanting to reach the limit.
In that case, Marcello is registered since more than 4 years...yeah, no messages but sometime lurkers can become really active... Anyway in the 'seller perspective', this wouldn't change too much, even if -of course- it's still better to know the games we are selling are going to the right hands