Depends where you are, and how much you actually want to make for your stuff! In my experience as a seller you need to be willing to let things go for cheap, take a range of stuff and if it has no prices on it then assume someone is going to take the piss, you will not sell more than half of whatever you take. As a buyer they can be great for picking specific things up for a good price, especially at the big ones, but a lot of the really good, or really cheap stuff sells between traders before the doors open.
The Chalfont jumble is a good one, nice size and usually has a good micx of traders and people who just want to empty the shed, next on is 2nd November.
