Unless the robber is presenting a weapon that poses a grave threat, I wouldn't pull my gun in that scenario.
*
Probably the best answer. Many of these places are too crowded to run the risk unless you have a pretty good idea that the robber is going to do something worse if not stopped.
If one is an LEO, the offender has no choice - they must submit or be forced by whatever means are reasonable under the circumstances. (Hence Dave Keith's response.) The rest of us have no legal ability to coerce compliance, so unless I can articulate perceptions that will essentially justify shooting the offender with little if any warning*, the winning answer is let them run away.
*Warning: there are a lot of misconceptions on this. Unless your state has some odd legal position (and I have never heard of any like this), there is no need to give any warning in a defense of self or others scenario. The 9th Circuit, based on arguments made by dishonest anti-police plaintiff's lawyers and not properly addressed by the incompetent LE defense Bar, has blended the
Garner (fleeing felon Constitutional case) with
Graham (general use of force seizure case NOT involving a fleeing felon) and ignored defense of self and others to state that a warning is preferred. That is utter drivel, AND it only applies to LE, not us. State law on use of force is what applies to us, and if you don't have a good idea of what the law is and how to assess the circumstances and then apply tactics, and then articulate it well, put away your guns and study.
I suspect I will more or less unconsciously give some vigorous verbal warning because we trained that way on the range, and frankly, spent a lot more time yelling at offenders as a means of control than actually applying force. That warning will be LOUD, partly because of my voice's nature and adrenaline, and more likely than not blunt to the point of crass due to my east coast potty mouth. If close enough to reach the offender (and I hope not, but circumstances dictate tactics) there is a lot of value to a palm strike to the most sensitive portion of their body I can hit as I draw with the primary hand. It buys time and messes up their performance. Note the technique I mention; unless you have a good background as a boxer, your punching technique is going to be sub-optimal and have a good chance of a hand injury that will degrade your performance.