If you mean difficult in the since of the customer is having a hard time deciding, then I would help them out by asking them questions about the situation or letting them explain so therefor I can help them solve that difficult situation. But behavior wise, I would negotiate with them, giving them a chance to stay in the store. This is exactly what I would say " I understand that...... but the faster you are under control etc.. the faster you can leave and not deal with this situation, or if you don't want to wait in line (or what ever the situation maybe). Then you can give me your items and kindly step out of the store." And if I have to, have the customer escorted out.