Help with uncomfortable situation with older male customer?

Being friendly is what we all need. There are too many stuffed collars out there in the real world. Maybe he likes the way you treat your customers and means no harm. Even if he does get flirty or asks you out, you should be able to handle the situation without causing hard feelings. As long as he doesn't become pushy or demanding, you will be ok. It is good that customers have favorites, and it should make you feel good. I hope everything is innocent in your situation and your customer is only friendly like many more need to be.