Use of a personal loyalty card by the cashier (Airmiles, Aeroplan or others) The cashier assumes that the company agrees to give it anyway, so if the customer does not take it, he believes he has the right to benefit from it.
To prevent :
Ensure that employees are made aware of the ban on this practice
Get crate reports containing all used card numbers more than 2 times in a single day
Use video recordings to confirm guilt.