I don't like the term haggle because it has a back and froth connotation. Coming from a sales back ground if someone is negotiating your price then you have failed to convince him that your services have that value.
Example: If I offered to sell a Jaguar XJR for $10,000, you would have many questions. What year? Has it been wrecked? How many miles? Is there anything mechanically wrong with it? Does it run? .... etc All because I didn't give enough information to convince you that buying a $70,000 automobile for $10,000 was a good value.
However, if I told you I just won a brand new 2015 Jaguar XJR in a contest and it has no miles on it, but I can't afford to pick it up because I don't have money to pay the taxes $4900 and the ticket is void after today, so I would rather get $10,000 and you pay the taxes and claim the car then get nothing at all and lose the car. Now I have given you enough information that you see the value in my offer. In the first scenario you are skeptical - unsure of the value - feel like there is a catch maybe. In the second scenario, the value is clearer and it all makes more sense and anyone with $10,000 would take advantage of the offer.
But, don't get mad at someone who haggles, take it as an opportunity to find out why they didn't see the value as you set it. Ask them questions. What makes you think I am not worth $400 per hour? Many times they will tell you and you can use that to better market yourself.
As a fellow sales person I have to warn you it can be brutal sometimes. Occasionally you find out that your product isn't quite as special in the market as you thought. And sometimes you find out that you had no idea what the client was looking for - what their hot button is - that your presentation really sucked. Sales is a brutal business. You can't sell everyone. But, if you don't take it personally, and try and learn from the ones you don't sell, then you will get better and better at selling your product and presenting you product and packaging your product ... business is business ... don't get mad - get better!