It's small if one is geographically constrained or one has risen up to a certain point on the promotion ladder. Beyond those factors I am skeptical that it's

It's small if one is geographically constrained or one has risen up to a certain point on the promotion ladder. Beyond those factors I am skeptical that it's worth worrying about whether a past manager will have anything bad or good to say about a person. Even if the chance were worth considering, I think one would do better to view it as a negative signal if a company makes the decision to not hire based on one bad or negative reference. It means the company was looking for any excuse to not hire the candidate, and it seems very likely in that case there wasn't really a good fit. This of course assumes that negative experiences are (relatively) rare. There are people who just can't help but torch the place everywhere they go, but no advice really applies in such extreme cases.