It depends how desperate you are for space. Selling on eBay (or similar sites) has the advantage of knowing that you'll probably get at least a few bids so, though you might not make much money, you'll definitely end up with less clutter in your house. Selling on, say, supermarket noticeboards can be a bit more hit and miss but you might get more money in the end that way. (For example, if you want the best price for that tent it might be best to wait until later in the year, when people are tempted to go camping, and then try to sell on local noticeboards).
While some stores seem to have done away with public noticeboards, and others aren't as widely used as they were in the past, some stores seem to have boards which are full of adverts, with lots of people stopping to read them. Wilkinson's is among the best.