We never paid babysitters when my kids were little. We took them with us, or didn't do it. On the rare occasion we HAD to do something and the kids couldn't go, my SIL or MIL watched them.
WARNING: RANT AHEAD:
$18 an hour??!! I didn't make that much money an hour until I had a bachelor's degree! holy crap!!
Despite what many on here are saying, it's not "cheaping out" to pay a babysitter less than minimum wage. Min wage was $4.25 when I used to babysit in HS (in the 90's), and the going babysitting rate was $2.00-$2.50/hr, and for that pay, I used to do a pretty good job! It's really not THAT hard to keep kids alive and safe for a few hours, so what do they need $18/hour for today??!!
Personally, I think that charging (and paying!) that much is insane, and like everything else, parents feel guilted into paying that much because they think that paying any less - and then something happening - will make them bad parents. Things are going to happen no matter if you are paying a 15 year old $6-$8 (which I think is much more reasonable for a kid to earn babysitting for a few hours) or if you are paying them $18.
But I get it - we are raising entitled kids in an entitled world, in an entitled time. They expect to be paid $18/hour to make some mac and cheese and put the kids to bed at 8pm, and sit around watching Netflix for a few hours. And parents agree to pay it. Why? Because it's SOOOO unheard of for a teen to be expected to keep a kid safe and fed for 20 bucks while their parents have a date-night? In order to provide these VERY basic duties, these kids have to be paid more than most of the parents started off making after college?
What a racket.
To those willingly paying that much, and enjoying doing so, more power to you. But don't fool yourself into thinking you are getting any "better" care for your kid. A 15 year old is a 15 year old, no matter how much s/he is getting paid.
YMMV.