The overhead bins are shared space; first-come, first-served. There really isn't much more beyond that. Many passengers have varying opinions about what additional rules should apply but it really is just about working together to get everyone's stuff stored efficiently. If more focused on that, instead of on defending their 'entitlements', we'd avoid a lot of conflict. It is good when the crewmembers can lead in that process and help find options that the passenger(s) may not have thought of.