Here's the way a service like NinjaBet works. To be clear, I'm in the US and this is all about US matched betting and taxes. I used NinjaBet, which is currently pinned on sidehustle, but didn't purchase a subscription and I'm not advertising the service.
Over the past week or two, I've been dabbling in and researching matched betting as a potential money-making opportunity. I've recently been trying to do some side hustles to help save for my kid's braces, college, etc.
Here's my review/thoughts on the tax implications and the process: This is not technically passive income, but doesn't take much work to 'make money'.
I see this posted every now and then in passive_income and wanted to chime in with some of my research. The sidehustle mod shadowbanned me for posting this information, probably because they have a pinned affiliate link at the top for NinjaBet and matched betting.