It's like any kind of start-up, you could make money quickly but it wouldn't be immediate and you'd have to leverage your labor before anyone would pay out. Obviously, day labor is easier provided someone needs the work you do and you meet them that day and are connected with them. Being online is the same, but worse in many ways because depending on what the skill is being offered, it's even harder to verify the person can deliver. Or worse, that you'll actually be paid by who says they'll pay idk.
I guess the biggest barrier to a smooth "day labour" practice on the internet is the verification of the person's skills