During the mid day, shops and businesses close down for siesta time. Depending on the individual shop owner, the shops will open back up between 3:00 p.m. and 5:00 p.m.
Be sure to get things you absolutely need in the morning before siesta time or you will have to wait.
Although a beautiful place, you can begin to find the piazza the ugliest thing in the world if stranded there during repozo. Times vary through the seasons and are especially lengthy in the winter. Make sure you have something to do in the early afternoon or know your travel arrangements well so you don't have to wait in possibly poor weather for the shops to open again.