A quick note on the numbers: they're just examples in a stand-in currency. Use your own, the math works exactly the same.
Search this question and you'll get answers ranging from "I made $40" to "I cleared $4,000," which is true and useless at the same time. The honest answer is that a craft fair day is a small, knowable equation, and once you can see the pieces, you can predict your own days and improve them. So let's build the number from the ground up instead of guessing at it.
Revenue is just four numbers multiplied
Everything you take in on a given day comes down to this chain: how many people walk past your booth, what fraction of them stop, what fraction of those who stop actually buy, and how much the average buyer spends. Multiply the four and you have your revenue. The reason two booths at the same fair have wildly different days is almost always one of these four, not luck.
A worked example with believable numbers
Say the fair draws 1,500 people. Your booth is mid-aisle, so maybe 60% wander past you, about 900. Of those, 15% slow down enough to look, roughly 135. A quarter of the people who stop end up buying, so about 34 sales. Your average sale is $18. That's 34 times $18, or around $610 for the day. A genuinely decent Saturday.
Now the part the big numbers skip. Out of that $610 comes your $50 booth fee, about $18 in card processing, and your materials, which for a lot of makers run a third of the price, call it $215. Add $20 for gas and parking. You're left with about $307 of profit. Set aside a quarter for taxes, roughly $77, and you pocket around $230. Still a good day. Just not the $610 it felt like when the cash box was full.
Then divide by the hours you actually spent
The market ran six hours, but you also set up, tore down, and drove. Call it a ten-hour day. That $230 is about $23 an hour, before you count the time you spent making everything in the first place. This isn't meant to be discouraging. It's meant to be clarifying, because $23 an hour is a real wage, and now you know which levers move it.
The levers, in order of power
Notice that booth fee was a small slice. The big movers are the four traffic-and-basket numbers, and the two you control most are the stop rate and the average sale. Getting a few more people to pause, with a better stall layout, and nudging the average basket up, with tiers and add-ons, compounds through the whole equation. Turning that 15% stop rate into 20% and that $18 basket into $22 takes the same day from $610 to roughly $1,000 in revenue. Same fair, same hours, same you.
A bad market isn't a verdict on your work. It's one data point in an equation you can read and adjust.
The catch is that you can only improve numbers you actually track. Knowing your average sale, your real materials cost, and your profit per market is what turns "I think that went okay" into "I clear $230 at this one and lose money at that one." Wares logs your sales as you make them and shows your profit per event after expenses, so each market teaches you something for the next. It's free to try, right in your browser.