My family always wears a mask properly in stores.sadly some wear below their nose or take off to talk on phone. if they have covid and cough or sneeze in a store can you catch it even while wearing a mask? its nerve wracking?

Unfortunately, yes: You describe common and frequent mis-wearing of masks, and this dysfunctional behaviour can easily infect bystanders. Suggest you use N-95 mask, and keep tightly on. You could add one of the newer clear plastic facial shields.

Yes: Masks can decrease spread of lung fluids/particles to the environment but are no guarantee they stop them all. The mask you wear protects others a bit more than you, but neither are completely protected. Some masks, like the N95 & higher rated masks do more, but they are not easy to find. Do what you can to protect yourself & loved ones. Get the vaccine when it comes.