Take care of the customers you already have and treat them like gold.
It's probably been said a 100 times on this forum and probably will be said another 100 times or more. But so few seem to get it.
We all know it takes either more time or more money to get a customer, then it will cost to keep one. You've already sold them once, statistics prove people will and do buy again. That is, until you blow them off.
I've lost count how many marketers I've never gotten a reply back from, either for something important or just a quick question. I'm not being a complainer, just the fact that many have lost my future business. I am also not going to recommend them to any one else.
Many preach about the backend being the silver lining, well if you can't take care of the front end, how much of a back end will there be? How much could you be losing?
Is every one of my customers happy? Probably not, that's near impossible, too many negative people in the world to start with. But I try my darn best.
While starting up a new site a while back, I unknowingly messed up the support system/contact system. There were several people who had problems and since they could not contact me, many thought I was just taking the money a running. Don't blame them. Not a good situation. I fixed the problem and replied to every one of them. I apologized, admitted my mistake and gave most of them something to try and make up for it. Did I save them all? No, I really doubt it, I'm sure some are gone for good. But, I have seen many of them back as repeat customers, several times. Even when you mess up, admit it and do your best to win them back, after all it's mostly likely much less effort and time then you take to get a new customer.
I spent a number of years in retail and I seemed to have a knack for smoothing over upset customers. I wasn't some slick talker or spin doctor, I just simply listened to them and usually agreed with them, saying they had a right to be upset. So often those people would come back only to talk to me. People just want to be heard and acknowledged, treated like a person and not just another sale. It's really such a simple thing, that could pay off 10 fold or more.