I have test driven a Ford Fusion 2004 model and the clutch seems to be slipping a bit, can they tighten the cable or do they need to replace the whole thing?
Welcome to the site @Angela. Slipping clutches are usually a problem with the clutch plate, the clutch is worn, oil leaking onto the clutch, or a binding clutch cable. There's other issues it could be, all requiring a mechanical repair. It's possible a cable adjustment could fix the problem, but it's a lot less likely.
There's plenty more fish in the sea and cars in the lot, if it were me I'd test drive something else.