what would you tell this person?

[ann]

if you think she is a pain now, just wait. It may be best to "fire" her before you even begin. Somethings just aren't worth the grief.

Even if she agrees to your present price, she will get 'even" with being a huge pain.
Some people just have to have the last word and the last word never ends.

 

[Steve01]

You shouldn't even consider dealing with hagglers. You will run into plenty of them, but you will also run into people who understand you get what you pay for. Save yourself for the people who appreciate your talent.

I wouldn't say that, there's nothing wrong with negotiating the best price for your purchase, I do it all the time.

There's also nothing wrong as a vendor to say, "I've given you my best price."