I wonder how much of the haggling is just a reflection of the low opinion many have of photography. They believe almost anybody can do it so why pay so much? Not many would consider asking the person next door to make a wedding dress but many will consider asking almost anybody to take pictures. Worse with digital I'm guessing now people will be looking at injet 8x10s and wondering why they should pay more.
Personally I think if you can't handle Aunt Edith and Uncle Bob with thier cameras you're in the wrong business. People will bring thier cameras no matter what you do. You can try to stress everybody out by banning them but I bet some body will still sneak one in.