If you were bursting with work and somebody stopped you in the street and asked for a quote you didn't really want to give you would quote a lot higher than your normal price because you are confident.
So true,
I once did a quote for this lady who was obviously well to do and lived in a 4 bed detached house. We were having a great laugh whilst she showed me around and we obviously got on. She came to us through reommendation of one of our existing customers.
Now the house was worth £15 - £20 and we would have been happy at that price. I jokingly said to my colleague, watch this, she will pass out!!
I told her "ok, you ready for this? (smiling) we are not cheap and you will get a good job, lets call it £40 !
She told me "yep thats fine !!!"

I laughed and said, "don't be silly, I was just joking! It's £20 and thats it!"
She laughed and said ok, but the thing was, she genuinely was going to pay it???
I guess it boils down to ask, you just never know. She has been a happy customer now for about 3 years.