Ok, here is my two cents for Farmers Markets.
If you are going to sell individually, make it a round dollar value ($2-$3). No one wants 50 cents jangling around in their pockets at a Farmers Market.
I personally would do samples and sell no individual cupcakes. Like very small peices of a cupcake in a mini cupcake paper (8-10 samples from one cupcake). Samples will get you SO much traffic, especially on your first few Farmer's Markets. Once you have a reputation, you could back off and have no samples and sell a few individual, but if people love your cupcakes they will buy a 4 pack or two or three. The thought process behind not selling individually is so you make up with volume for giving samples. If I tried your cupcakes and loved them, it would be no problem for me to buy a 4 pack.
Also, do as many combos as you can. For example if you are selling singles do one for $3 or two for $5. People make snap decisions when it comes to sweets and Farmers Markets. If I wanted one but my husband was on the fence, but I could get two for $5 I would make him pick a flavor and get two.
Also, do combos for your larger packages. So like $10 for a 4 pack but $15 for two 4 packs. If I loved the chocolate sample, but my husband loved your caramel, I would buy two different packages if I got a discount.
This will help increase your overall volume and help your customers enjoy more than one flavor.