Definitely first have a phone call to weed out people who just aren't a good fit (they aren't available when you need them, they don't have experience with your age kids, they don't drive and you need a driver, their parenting philosophy is very different from yours, etc.) After that, I'd say definitely do a paid trial. I have always first hired babysitters as "mother's/father's helpers" to play with the kids while we are around and just doing other stuff. If that goes well, we work our way up from there.
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