Without an account of that, IBE is the claim that something being the best available explanation is evidence that it is true.
That being said, we typically judge the goodness of a possible explanation by a number of explanatory virtues like simplicity, empirical fit, consistency, internal coherence, external coherence (with other theories), consilience, unification etc. To clarify and justify those virtues on other (including Bayesian) grounds is something epistemologists work on.
Without an account of that, IBE is the claim that something being the best available explanation is evidence that it is true.
That being said, we typically judge the goodness of a possible explanation by a number of explanatory virtues like simplicity, empirical fit, consistency, internal coherence, external coherence (with other theories), consilience, unification etc. To clarify and justify those virtues on other (including Bayesian) grounds is something epistemologists work on.