No-one is advocating leaving their dog with a total stranger, are they? What are they doing, pulling up outside someones house, chaining their dog to the front door with a note around its neck saying "back in the three weeks", and driving off?
No, it's like any business transaction - you vet (sic) people just as you would for anything else. While some dogs can be nervous nellies, most aren't. They're not cowering under kitchen tables afraid of seeing new humans. Hell, my dog wants to meet and know every damn human he see's on my walks.
If I were recommended a neighbor to dog sit, I'd go and speak to them. I'd ask other people in the area I know to see if they know anything. I'd google them. It's not rocket science. Just because a name is found on an app, doesn't mean none of this happens.
It's great if you can, but it's not always possible. I did a lot of international flying, and there's no practical way to do that with a dog, what with all the regulations involved, then having to find hotels that accept animals, and so on. When I moved from Texas to Germany however, I did take my dogs at the time. It was costly, and lots of paperwork, but worth it.