Perhaps there's an Aztechnology tactical team waiting for them when they come outside, and there's a few moments of confusion when the team thinks the runners are the robbers.
Maybe the store doesn't get held up immediately, and instead one of the runners becomes the 1,000,000th customer and wins a lifetime supply of Nerps?
Maybe the store has hidden gun emplacements because they've been robbed a whole bunch of times, and someone hits the Panic button to make the gun start spraying APDS rounds at everything that moves more than 1m per Combat Turn?