Mate you know I'm a financial advisor don't you? I've been working with estate agents and surveyors for years! PM me what you are buying, rightmove link or something.

I'll give you some proper advice later, but the first thing that stood out to tell you to be careful with was the fact you are going to get the vendor and selling estate agent to do some investigations to confirm the problem. They will not be working in your interest, so put simply, cannot be trusted.

Rising damp does exist and can be a slight issue, but remedies can be cheap as long as you spread the work around properly. Damp specialists like Herritage charge an absolute fortune for things like plastering. Damp isn't always damp as such though. As in, it's caused by something simple like a loose flashing outside.

If the surveyor has flagged it, especially on a basic survey, then it's worth looking into properly. It's not everyday you spent £x amount of thousands of pounds.