Never pick a fight you can't win.

Never underestimate your opponent.

I know cliqches but a truism is a truism.  No you can't bank on a robber not shooting you anyway even if you give them the money.  A dead witness makes a poor witness.  You can bank on them shooting you if you are attempting to draw down while they have you in their sights.  

It's a tough call and only one you can make at the time.  

Of the incidents I have followed over the years that the good guy came out on top there was always certain things they all had in common.  First and foremost the badguy always had the drop on them.  Then it was either they got lucky and the badguy missed (not a happy thought to count on) or the badguy got distracted and gave time for the goodguy to pull down and fire without hesitation.  It's kind of hard to get details on those who tried but failed.  

Sorry I can't be more helpful.  The only time in my life I got the opportunity to pull my assailant gave me a wide path by not only pointing his gun in an awkward direction but even looked away.  I considered that really lucky at the time.

Tj

You have already taken the first steps for your personal survival. You have armed yourself, done some training...at least you apparently shoot IDPA, which is far beyond what many others do...and you are actively thinking about the issue. Good for you.

"Robbery", in my state, and most others, is defined as "taking by force, or the threat of force" and is thus a crime of violence directed against a person. (If the cashier turns his back and the perp grabs money from the cash drawer without saying a word or making any threats and then runs, that is "theft") In the case of a theft you usually are not legally justified in pulling the trigger...robbery is a different matter, especially if there have been several recent documented, robberies nearby where clerks have been shot after offering no resistance.

My very first recommendation is to give some serious consideration to whether you need this job badly enough to continue placing yourself and your family in such jeopardy. If the honest answer is "no" then simply find a safer part time job...in other words, don't BE there when the robbery takes place unless you absolutely have to.

If the answer to the above question is "yes", then I would recommend that you find yourself some good concealable body armor and use it. Look in the EE and you can find some good to excellent deals on slightly used vests. Kevlar, if taken care of, will continue to work as designed well past the 5 year "expiration date" of most body armor. A vest is not magic, but it certainly can save your life under some circumstances. For sure it is better than NOT wearing a vest.

The issue of "what should I do?" is, as others have pointed out here, your decision to make, and muct be based on what is happening at the time and place in question. No one can make that decision for you. Are you willing to place your life in the hands of a doped up thug...maybe even a juvenile gang-banger with no more conscience than a rattlesnake...who has already proven by announcing a robbery, that he is willing to use force against you to take what he wants? If you wait to actually see a gun, or worse, wait until it looks as if he has decided to execute you, it may already be too late.

Experienced stake out cops will tell you that there are at least three stages to an armed riobbery (in a more complicated bank robbery or such there can be more than these, but here we speak of a typical "Stop & Rob" market robbery, etc.). The  "look it over" stage, where he / they check the store out and decide it is good to go; the "confrontation" stage, where the robber(s) is usually as tight as a banjo string (often they are high on dope as well, since many need the drugs for "courage") and may be prepped to shoot at the slightest hint of resistance. Once they have the money, however, most will make a mental "shift" onto "getaway" stage. This is the instant when...if the decision has been made to confront... officers will undertake that confrontation. By doing so, they have bought themselves a slight advantage, because the BG now has to do another mental "shift"...they are now "inside his OODA loop".

If you wait to see or hear some direct threat of your execution before acting, the BG has probably gotten inside your loop, and now you will be forced to react to HIM. Should that happen, my guess is that the last thing he will expect is agressive, overwhelming force being directed at him by his victim. Realize that once you have started, you must be willing and able to carry this through to the end...even if his two buddies outside come running in to help. (Not the usual response, but not unheard of either). Running out of ammo, weapon malfunctions, etc. will probably get you killed here...plan for the possibility. Lateral movement, use of cover, positions of advantage and "staying in the fight" are all important. (Can you arrange the store layout to provide an advantage for yourself?) If the situation is not resolved after the first few rounds, "firepower" becomes increasingly important. It could come down to who has the last bullet or shotshell...make certain that is YOU.

Possible civil lawsuits are part of the risk, as is the more remote, but still very real, possibility of criminal prosecution. The "standard of proof" in a criminal case is "beyond a reasonable doubt", but in a civil case, it is "the preponderance of the evidence"...a much lower standard. You might want to spend the $150-300 or so required for an hour of an experienced criminal attorney's time and get his or her advice on the legal end of things before you have to pull that trigger.

Still think you really need that part time job?