I've used Trusted Housesitters - https://www.trustedhousesitters.com
I've had good experiences, but I will say that general consensus is that 99% of sit go smoothly and the other 1% are absolutely batshit. It's 100% on you to vet the homeowner. The company takes no responsibility if something goes wrong.
For how long?
This year I spent 8 months housesitting. 5 sits total, with the longest being 3 months.
I also imagine getting someone to trust a new user of the app would be quite difficult.
Yeah, getting the first sit is typically the hardest. I personally got my first sit fairly quickly and I got my second sit before the first sit ended (i.e. before I had any reviews), so it's doable.
>When you say to vet the homeowner, do you have any methods in particular?
Always do a video call (to check the Wifi) and ask for a virtual tour (to make sure their place matches the pictures on the site). I like to ask about construction in the area, the pet's schedule, medications, vet history, etc.
One thing to remember is that you're trading your labor for accommodations, so A. make sure it's a fair trade and B. avoid people who think you work for them.
>Are the sitters able to review the homeowners as well?
Yes, sitters review homeowners, so make sure you read the reviews (and the listing) carefully. A lot of the most entitled homeowners will give themselves away in their listings.
If you haven't started DNing yet you might want to do a couple of local sits to get reviews.
Also housesitting is considered work by immigration officials, so don't mention it at international boarders.