Best way to earn $100?

Work a job that you like or look around in your local community and see what you are good at and offer a course in it. For instance, I helped older people in my neighborhood how to use the internet and their cell phones. I charged 10$ per hour

HOUSE SITTING

PET CARE

DOG WALKING GARDENING

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Try to sell some of your items on eBay

I have some wrinkled up balls, if you lotion them for me I might pay you with one of my jizzed in $100 dollar bills

Do Uber, Lyft, DoorDash, Postmates, GrubHub, Jimmy John’s, GoPuff

become a street walker for a night.

I'll give you $100 to rub cocoa butter on my nipples

"Best" is subject to personal interpretation. There are a few who would be happy to do unsavory things for $100.

The most common response might be to "get a job."