It’s funny, you’d think, from reading about planning poker that the purpose of this exercise is to come up with accurate estimates. I think that’s missing the point.
The estimates are a useful by-product, if your organisation values such things, but actually the most important benefit you get from planning poker is the conversation. As part of the exercise, you explore the story as a team, and uncover any misunderstandings about the scope and depth of the work to be done to satisfy the story. The result of this exploration is a shared understanding of what the story means.
There are other ways to have this same conversation. My favoured practice is to hold a specification workshop where the team explores the scenarios that a user could encounter when using this new functionality. These scenarios are a much more useful product, to me, than an estimate. They give me a starting point for writing my automated acceptance tests, and they also give us all a concrete reference point as to the scope of the story. If my organisation needs estimates to be happy, we can count the number of scenarios to give a realistic feel for the relative size of the story.