Let Γ be a relatively hyperbolic group and let µ be an admissible symmetric finitely supported probability measure on Γ. We extend Floyd-Ancona type inequalities from [11] up to the spectral radius of µ. We then show that when the parabolic subgroups are virtually abelian, the Martin boundary of the induced random walk on Γ is stable in the sense of Picardello and Woess [28]. We also define a notion of spectral degenerescence along parabolic subgroups and give a criterion for strong stability of the Martin boundary in terms of spectral degenerescence. We prove that this criterion is always satisfied in small rank. so that in particular, the Martin boundary of an admissible symmetric finitely supported probability measure on a geometrically finite Kleinian group of dimension at most 5 is always strongly stable.This can be written as P f = rf , where P is the Markov operator associated with µ. Every r-harmonic positive function can be represented as an integral over the Martin boundary. Precisely, for every such function f , there exists a probability measure ν f on ∂ rµ Γ such that for all x ∈ Γ,In general, the measure ν f is not unique. To obtain uniqueness, we restrict our attention to the minimal boundary that we now define.