Good decision, manager. Indeed, the project owner's priority is to have best people to promote his project. It makes sense because promoting a project with quality members should be more effective, gaining people's trust, and probably getting more attention by potential new members. In correlation to merit, AFAIK, commonly who got more earned merits may show us how good they are. But never blindly to assess it, looking deeply their post history and their habits are a must.

However, regarding choosing the participants to promote the project is an absolute right of the bounty manager. We never compare one bounty manager to others as each bounty manager may have their own way. So, what ever the decision you made, the participants should accept it without complaints, as long it is fair and doesn't broke forum rules.

That's my own opinion. Hope it can be useful. Thanks