Just about the only way I've ever made real money has been online in the manner you're talking about.

I enjoy thrifting and flipping, which is harder than it might seem to be successful at. It requires familiarity with what a good quality item is, a robust knowledge of the kinds of prices you might get for those things and some knowledge of refurbishment. Most flippers will pick one or two things that they specialize in, usually based on an existing hobby, because they already have a baseline knowledge of it by being interested in it. Being willing to clean, replace parts, paint, fix or otherwise renew the item is usually the most consistent way of making a return on investment that might make it worth your time. However, there really are some golden opportunities which sometimes appear and another needed skill is being in tune to where those show up. The estate sale of some eccentric artist who has an amazing antique collection, or the office that's liquidating a bunch of computers or furniture, will be advertised briefly in some narrow window of view and time unique to your location and to catch it you need to be quick to act and decisive. I made a ton of mistakes early on and learned to be a lot more careful about impulse buying, but I also got good enough at it to make rent.

The other part of being self employed is the dual edged sword of freedom. You are never at work and yet you're always at work. There's no time "off" anymore, any day or any hour you might find yourself working and it's unrelenting. Unless you are remarkably disciplined you will probably never have a "weekend off". There's no meetings or bosses to answer to but that also means that if you mess up there's nobody else to blame but yourself. It has its own challenges and drawbacks, so don't let yourself be fooled into thinking you wouldn't find new things to piss you off.