The reason we allow non-members to post classifieds is so that you the members have a better selection of items to purchase. Ads are identified whether they are members or not so you have the option to not purchase from non-members if you wish. On the listing of ads member ads are marked with a red asterisk on the right. When you look at the ad itself it says at the bottom if it's a member or non-member ad. The whole reason for allowing that is to provide more service to the members.
BTW, non-members cannot read what is written in this forum. There are several member only forums that non-members cannot view at all (Truck '911', all of the FAQ forums, 1st support support for discontinued parts, pay it forward, competition, other, politics, and website). We will be further restricting how many threads non-members can view in a day and how far back they can view soon as well.