I'm not going to help a blind lady in the store.
Why won't you help her?
It doesn't concern me. The employees can help her, if she needs something.
It's polite, friendly, and expected to help people who are unable to help themselves. Practicing empathy is key here: if you were in the dark, and alone, without being able to see anything, would you want a stranger to help you locate items?
I would not need help in that situation.
I think that you would need help there. It will not take up a lot of your time; helping her is the right thing to do.