as a consequence of your mods bringing this to my attention:
Number of ads per week reduced to 10 from 14.
Believe me, getting free money for hosting is always a plus but one has to consider that the Classifieds are a way of on-boarding new members who head over to the forums and have a discussion, not as a way to make money. We've spent all this time discussing people spamming the Classifieds only to let retailers pay their way in? Seems a little silly, but I understand your point.
The return to the forum is - as mentioned - the fact that we are one of the premier places to list airsoft goods (and buy them). This attracts new traffic to the site (a fraction of which might stick around).
In terms of making this a paid service and the logistics of that, it's actually not too difficult. IPB already has ways of letting you pay your way into a group and from there it's just a case of restricting posts per group (something we already do, because Supporters can list an unlimited number of ads per week). If you're a supporter, please go here to discuss further.
The only way to 'bump' is to relist your ad after it expires.