If someone is interested in Fords then generally they will be a member of this site, if they wish to advertise they need to be a gold member, the idea of this would have been to stop x amount of users signing up just to advertise a car or parts for sale, this would have flooded the sale rooms with crap from people who's only interest in the site was to sell, not be a part of the board & put to other areas.
Advertising for non members means people who don't use this board, if it was a relation/friend who has something for sale that might be of use to members of this board who otherwise might not see it advertised.
there is normally someone breaking the rules, you can normally tell when a gold member puts a car for sale for sale then one of thier friend, a non gold member answers all the questions.....