Look at the paper thingy lining the bottom. That thingy should be clean and unmarked. Strawberries ripen after being picked so you don't want to select the ripest berries unless you want to eat them quickly.

Like with most produce it is about knowing how to select them. In many cases there is a national group/council for whatever fruit, nut ir veg you are thinking about and they have guides as to how to best pick things and what season to expect the best produce.