The two equations (First and last equation on page 145) are consistent with each other.
If the scattering potential of some atom is approximately a delta function then we would write
V(x) = f delta(x)
assuming this atom is at position 0. Plugging this into Eq. 9 just tells us that f = f (the integral kills the delta function) !
The reason this is not always trivial is because scattering potentials are not usually delta functions (at least in the case of X-rays). Eq. 14.8 and 14.9 will always hold true. But the expression
V= sum f_j delta(x - x_j)
is only true if the scattering potentials are very short ranged (you have a bunch of atoms each giving a delta function at its own position x_j and each having a strength f_j).
Does this help?