1. You half-ass tasks. Sorry to be so blunt, but it is true. If you perform at your highest level upon first signing a client, but months or years later you could care less if the product/service is amazing or of quality then you've lost focused and are denying your customer what he or she is entitled to.
2. You believe the customer is always right. Um, no. The customer may think he or she is always right, but they're not. You wouldn't sell a standard kitchen oven to someone who wanted to open a bakery would you? No, of course not. If you see a client making a mistake and you don't step in- you're failing that customer.
3. You avoid the evil client. If you ditch a client because he or she is too demanding than you might not be up for the challenge of expansion. Try your best to handle evil clients and resolve inner-conflicts before giving this type of customer the boot.
Dealing with customers isn't always easy. You are not going to have easy clients in life. There will be difficult clients and situations. Remember these three tips and make sure the problem isn't you.