That Vanish is good stuff, it even takes the colour out of the carpet...

A least you aren't answerable to her any more. On the one occasion I refunded half the money back, the lady threatened to tell everybody how bad I was at my job. (They had flooded the carpet prior to me cleaning them and lay the fault of the rotting underlay on me!)

"That's fine!" I said, "I've recorded our conversation on this phone, so you'll be hearing from my solicitor!" (A regular customer)
She soon started back peddling....

I can usually sense these odd ball/awkward people and up the price considerably, so as to lose the job or at least if I get the job, it's almost worthwhile.