Smoke me a kipper, Fidgits...
I'm not averse to spending money to advertise my car and I've every intention of putting it in Autotrader.
However, when selling my previous car I got an all-singing, all-dancing advert in the Autotrader online and two editions of the regional mags, only to have someone who saw it on the Owner's club forum actually buy it. So based on that, I favour my odds on the forum. Except that one was free membership, no holds barred.
However, before you start jumping to conclusions and thinking that I'm not willing to pay for anything, please take a moment to consider what I'm actually saying... what I'm paying for is a membership that I won't actually need, once I've sold the car.