Know Your

The sales manual says that you need to know your customer.
The Army manual says that you need to know your enemy.
What if your enemy and customer are the same person?
I mean, what if your customer wants to kill you?
Or your enemy wants to walk into your store to buy a toaster.
I hope you’d know that already.
Since you’re supposed to know your enemy and know your customer, right?
I suppose the most important thing is to know when your customer is not your enemy.
Otherwise, you’re going to look silly, attacking them with that toaster.