I've never had a garage sale but I do sell things on eBay and on Gumtree. I don't make much money because I sell odd bits and pieces I no longer use. I find that Gumtree is easier to work with and, unlike eBay, does not charge a fee when an item is sold. If I can't be bothered posting an item online, or an item does not sell, I usually take it to a Vinnies shopfront.
I'm the same re Gumtree and have a system where I drop the price by $5 after a few months of having to renew them each month. Then I'll make them free, a lot goes then and only after that, of no views/takers do i take them to an op shop if the item is worth that.
I'm constantly getting new stuff in to list (finding things in hard rubbish piles in my junk mail rounds) and have limited space.
I did try a garage sale last year in the Big Garage Sale weekend but it wasn't that successful for me because I'm down the end of a block of units and no one can see it from the street, despite me putting out signs.
I have sold things on ebay, but for the amount of money I got for them it wasn't worth the time it took to list them. It might be more worthwhile for larger/more expensive items. I have had a garage sale and that wasn't terribly successful either.
I sell very cheaply, to avoid too much time on questions etc, but I sell a lot. It started because I thought it wouldn't end in the landfill if they paid for it. Now I fly to Singapore for the Grand Prix on the proceeds, so it's win/win all round (I know, saving landfill, destroying the environment with excessive petrol)
I've sold on ebay/gumtree, and I've held garage sales, successfully in the sense that I got rid of the things I didn't need, but I didn't get wealthy on the cash. Another thing I also do is give hand me downs to my relatives and friends as my children outgrow their clothes. And they love receiving them.
I just show stuff that I want to get rid of to my friends whenever they're over, and if there's something that's really precious/expensive, then I sell it to them, else I simply give it away for free :)
Had a garage sale at my place once to help a friend sell his stuff. I swore I will never have a garage sale again. When we moved houses I sold most of my furniture on e bay and it was a breeze! e bay I most certainly will continue with. only to get rid of stuff. Both Garage sales and e bay wont fetch you too much money if you are selling old stuff ( selling antiques is different though)
I've used ebay, gumtree and garage sales all with varying degrees of success. I think it depends on the item and your pricing more than the place. Things I can't sell go to a thrift shop, school trash and treasure stall or I leave them outside my gate for a week. LOTS of stuff has gone that way.