[QBFimi]

>> Does a person have a responsibility to a store clerk they don’t even know?

Then the Lord said to Cain, “Where is your brother Abel?” He said, “I do know not; am I my brother’s keeper?” Gen 4:9

[Blue Jays]

Much of it depends on what one truly feels is the opportunity for success.
Standing in the queue, unarmed, without knowledge of the robbers allies...that is a risky proposition.
If a family member or friend is with me and they are directly threatened...that is another factor favoring a fight.

If one is alone, near the exit, and can just duck outside?
Nothing wrong with employing that technique in an uneven fight.
My family and friends would prefer that I be alive rather than taking a truly large risk to life and limb.