The best way to identify the most appropriate rationalisation
The selection of the correct rationalisation can sometimes be the hardest part of your interview strategy. Rapport building can help to overcome that problem. If you are able to make a connection with your subject while developing rapport, you can obtain some great input and indicators into the source of their current decision making.
Remember, the proper rationalisation helps overcome resistance. If you have direct input from your subject, you can better determine what may cause them to make the decision that put them in this situation in the first place.
For example, if your subject starts discussing a new purchase they made, a relationship that just started or just ended, or bills not being met, they may be having some financial issues. Maybe they start talking about their flatmates or friends and how often they come into the store to hang out which could cause some peer pressure. If the subject starts talking about their work hours getting cut, or complains about the management maybe they are acting out of revenge because they are disgruntled.
Sometimes your subject is giving you the answers you need before you even ask the question – all you have to do is listen.