They are „advertised“ by hanging a broom outside (Besen is broom).
You tend to go visit a few over an afternoon, because they concentrate on certain wine-making towns.
Can't imagine the food safety institutions even considering pop-up home cafes in my native Belgium.
Many states in the US have "cottage food" laws that allow low-risk foods (think baked goods, jams, jellies, candies, nuts, etc) to be labeled "this is an unregulated unlicensed cottage food product" and sold without a license. Belgium may have something similar.
Not Estonian, but a Swedish fellow I knew always had a summer event with lawn darts and other odd games and food each summer