Whilst PPRUNE may be a news forum for professional pilots, that doesn't invalidate the thought that professional pilots might want to buy or sell something - their CPL text books, perhaps, or the DC headset after upgrading to the Bose; or they might want to buy something - from a nomex flying suit to a whole aircraft or a share in one.
I don't follow the idea that advertising something makes you legally liable for it. If I advertise my car for sale on Carsales, my house in the Sydney Morning Herald, or buy a boat I've seen advertised on Boatpoint, neither I nor the other party are going to have much joy in suing the publisher if the roof leaks or the mast breaks. And whilst you might argue that this sort of classified ad is not news, newspapers have made a living out of it for hundreds of years.