Collection company will not put offer on paper?

I just spoke with a collection agency and the lady there made me an offer to delete my negative credit report but said she will not put it on paper and that she gave me a "verbal agreement". I told her that is not good enough and that i need something on paper. She refused and said i have three days to accept or reject it. I torn on this as the offer is exactly what i want, but i have no paperwork to show for it. She said she will send me a paid in full letter only after i make payment. My primary concern is the DELETION of the negative credit from my report. Should i go ahead and settle with them?