I'm signing up as a vendor at a family fall festival in November. There are over 100 craft and home business vendors! It's their first year doing it, so I don't know how many to expect. However, I would guess several hundred - 1000. I sell decorated sugar cookies, and I have no idea how many to prepare for that day! Is there a rule of thumb for the ratio of people who buy? Thanks!

I vend with a dessert truck.  The rule of thumb is that 10% of attendees buy desserts.  It's not absolute, but many fewer people buy dessert than you'd expect.  It's completely discretionary and everyone is always "on a diet."