This is social dancing, not practice. Perhaps they see or feel something that you do not. It is okay to talk during a dance and you might learn something valuable at the same time other than where the person is from. There are some people who have no plans of ever taking lessons. These people depend on sensitively made suggestions, informal intermission time lessons, and experience to become better dancers.
Dance is a marvelous from of social interaction.
It can make you many friends - or it can isolate you from the very people you would like to know. Don't criticize a partner no matter how much you would like to. It is not enjoyable to have a partner with whom I've just had a blast dancing with apologize and make comments that she needs more lessons or something like that. Sometimes this happens when they made a few mistakes, usually which a bad lead had something to do with, or I've led them successfully through things they weren't familiar with but they followed beautifully. Dance to the understanding level of your partner to the best of you ability.