I got a note from a young guy the other day that was an absolute priceless gem. The short version of his email said that he had finally come to realize what he was worth to his clients. As a result, he now quotes a price for a job to his client and says to himself when he does, "This is not my best price, this is my only price."
Accepting that principle as a contractor is a huge step in your development as a business owner. Unless and until you believe that in your heart, you will always be tempted first to worry about your price and secondly to cut your price before you quote the job. Even worse is cutting your price after your initial quote, which in almost all cases will destroy your credibility with your potential customer.
If you have done a good job of estimating the job, and you know what your overhead expenses are and what you want to make as profit on the job, then there simply is no place to cut your quote. Again, until you believe this principle, you will always have that hobgoblin hanging over your shoulder and more often than not, the customer will pick that up. Sales is attitude, attitude and attitude. Your attitude towards your worth and what you should charge for your service will go a long way in determining your success in this business.