Almost right away, I got the $20 voucher. It was delivered online and I printed it off the website. Then I had to wait a few days to use it because the farmers market wasn't open until Friday. The printout explained the procedure. I needed to visit the market office on the upper level to exchange the voucher for four $5 gift certificates. That's actually pretty handy because this way, I didn't have to use all $20 at a single store at once. I can pick four different stores in the market if that's what I wanted. The clerk knew right away why I was up at the office. He had a long list (4 pages) of names of people who had bought that Groupon deal. He found my name in the list, checked it off, and handed me the gift certificates and a map of the market.
I used one of the $5 certificates this evening to buy 8lbs of oranges. Produce isn't too expensive at the market but 50% off makes everything really cheap. I decided to save the other three certificates for another time since these are valid for six months.