We use house sitters - to look after our dog.
You can set yourself up as a house sitting 'business' - but if you want any gigs, the only way you'll get them is through the usual house-sitting websites.
When we need someone we go onto X site, scroll through all the names, see who's available for the dates we need, and then select a few that we like the look of.
I would never going onto ONE house-sitter's website, as I want to be able to scroll through and see who I like. And going into one's person's site - they're probably not going to be available on the dates I need them, so I want to be able to select from a long list.
If you don't want to look after animals, you're pretty much dead in the water.
And you can't bring someone - a child, say - on the basis that the homeowners won't find out.
You have no idea what sort of security they might have, how close they are with their neighbours, how many of the friends might wander by, to discreetly check on the place, etc.
You lie about who's at the house - your house-sitting reputation is in tatters. and your reputation is all you have going for you.
The entire thing is based on a trust model, so if you're even vaguely untrustworthy, you're not fit for purpose.