Depending on your area farmers markets can be tough. If you really want to
sell produce the first thing you have to do is decide what is your goal and why would anyone pick up your tomatoes. This gets you to the idea of your farm. What are you selling points. If you are just producing vegetables like everyone else and your booth looks like the rest then you are going to run into problems. My partner spends a lot of time designing the layout of the booth. From the tablecloth to where the carrots will go. Look around the market and see what people are doing well and what you think you can improve on. If everyone is growing the same thing can you try a different variety that looks different and draws people in. Can you add season extension so you have something a little sooner then everyone else.
One of the things that really bothers farmers is people who come to the market with there garden produce and then sell it at way to low a price. If you can price lower then everybody else great. But make sure you are really thinking about the cost of your goods.
