A somewhat confusing "local custom" are the numerous Erotic/Sex shops in Liberec. I was very surprised to see so many of those even in the city centre. You find them every 100 m, sometimes two or three in that distance.
I cannot imagine the Czech need so much stimulation for their sex life. Or is it all for tourists? I really don't know.
Every friday there is a market on the square in front of the town hall. Craftsmen from the region offer their products.
Expect low prices and good quality. I bought some pottery, a typical product of the area. But you can also see folks selling Bohemian crystal glass, regional food etc.