Auto flood damage help,,Please?

I really need some help. We got a car yesterday from an individual. When we first looked at the inside it looked a little dirty and smelled very clean, strong but clean. The outside looks great and run great. After about an 2 hours or so we signed the papers. We got in the 2000 Montero Sport to go home and there was a noticeable musky\sour smell. After about 4 hours the smell was so bad that it makes me gag. I pulled a piece of the carpet up and there is sand and brown stains that kinda look like water marks. I was lied to. I was never told about the smell or any flood damage. What should I do? Can I cancell the deal?