The others have described the problems. There is no guarantee the work you describe will fix it. If so, then why doesn't the present homeowner do those things and guarantee that it will work before you buy. Sounds like he knows more about the problems than you think and that is why he is trying to sell it.
That said, if you otherwise like the house, price it like one without a basement as the basement may not be usuable for living space. That will save you beaucoup thousand. You couldn't finish it with those moisture problems.
And if all else fails, stock the basement with catfish when it fills up.