I'd vacuum the floor. The just use any ordinary household general purpose cleaner or laundry detergent. Depending on the condition, you might want a little action with a scrub brush. Rinse it well a couple of times and allow to thoroughly dry. Any home center or paint store will sell flooring paint. Just follow the instructions on the can.

be carefull...if you get a lot of moisture thru the concrete it may cause you paint to peel leaving you with an even bigger mess to explain. I would just leave it go. Foundations crack. Freezers can leak. Its all understandable. If anything, put an area rug in place. If the crack is REALLY big it likley should be listed anyway. Your realtor should be able to help with this.

I second Mike's idea. We did that in our basement, just as he described, and it's held up well. We just used some sort of latex floor paint, avoiding the more durable epoxy stuff.

Alternatively, if it's smooth enough, clean the floor and just put down some self-stick vinyl. Lots of contemporary stuff to choose from. One of my clients did that in the dark, dingy unfinished laundry/utility HVAC half of their basement. It looked great and held up very well (for the two years that I was able to witness before they sold, anyhow.)