Best advice I can give off of my short 3-4 yrs. experience:
Stick to your guns no matter what. Don't cut dishonest or cheap customers any price breaks. When dealing with good, honest customers, cut them deals whenever you can. When a customer tells you that they are accepting bids either end the conversation right there or instruct them to never contact you again. Not only will you be saving yourself the pain of working for such people, you will also be saving your integrity and moral strength. Don't engage in the degeneration of our industry. Be proud of what you do and who you are.