It used to anger me but it makes me laugh. Thing is, they really really want to see you, but cannot afford you so they either become bitter and send you an abusive message such as "You must be up your ass charging that" or they try to haggle. Never works.
I had one email me saying "Your rate is too much 100 an hour is better" I said "Thanks for your concern but I get more than enough business at my rate, if you cannot afford me and can only afford 100 for the hour I can recommend some lovely girls within your budget" he never replied haha! An old regular moaned about my rate a few weeks back as I've increased it, and I said to him in the booking "if your boss decided to pay you less on your wages would you be happy?" He said no and apologised. They want us to work for less to suit them but they wouldn't in a million years do the same in their line of work, and guaranteed if their boss increased their wage they wouldn't object! How hypocritical.
I'm pretty sure they don't stand in Tesco moaning that their monthly shop is less in Asda or Aldi!