If the lack of a gutter is the biggest problem with this house then
you don't have a lot to complain about.

The seller does not HAVE to do anything. You can buy the house as-is
and then YOU can install the gutter yourself. Installing a gutter and
a downspout is not a huge expense.

The grading at the foundation is a bigger problem than the lack of a
gutter. Properly graded the runoff from the roof will flow away from
the house rather than puddle and seep into the baement. A good mulch
will help dampen the water so you won't get splashback on the house.