Shaun Clowes shares some really good hiring advice in his post Picking good Product Managers – insightful interview questions. He starts it off with a good reminder that “bad product is worse than no product”:

A product manager without a systematic approach to their discipline has less context than the team members so is less likely to make good decisions naturally. Thus a bad product manager is more likely to cause the team to make mistakes than no product manager at all.

The worst part is that many experienced product managers will be convincing since they’re used to influencing organizations. No matter how convincing the vision a product manager might paint, they need to be able to justify it within the competitive environment, the strengths of the organization, the data that proves the market exists etc.