It's extremely important that you keep a "hand on" relationship with those you are involved in business with. Not just paper mail like invoices. You are doing it right. It puts that personal touch.
People tend to gravitate towards people that appreciate them. The smallest things you do make people happy. And it keeps them coming back.
If I can buy a soda here for a dollar and they guy is a cock, but I buy the one for a dollar twenty five and I sit down, shoot the shit, talk about bitches WITH the guy that sold it to me?... and then guess what?
I'm out of fucking soda? Im loving it for that moment.
Where did the Coke go? "I'll take another..."
Good business...
