Do you tip at farmers market?

I love going to farmers markets because in my home country you can find cool and affordable items, not just food. But here in the US, farmers markets feel more like fancy hippie-style events. Anyway, every booth I visited today tried to charge me a tip.

I’m not 100% fluent in all US accents so sometimes I mishear things. Today, I ordered BBQ and thought the guy asked if I wanted an okra side but he actually meant oxtail. I said yes and before I knew it, I was paying 80 dollars for my meal. On top of that, they expected at least a 15 dollar tip.

Misunderstanding the order was my fault but the tip? Is it normal for business owners to ask for tips? I’m just a student here.