The template sets included in the classifieds are For Sale, Wanted, Help Wanted, Personals and Business. Technically speaking I guess that would be considered buy/sell.
Technically speaking I have no problem adding in such functionality in a future version but I would need alot more information on how such a thing would even work. There is a contact seller feature where you can email so I assume you can contact the seller and say hey I will trade you a pair of boots for that hat. Without Pricing or anything like that you can not pay for anything you basically take alot of functionality away from the software and basically your talking about human interaction person to person.