Picture posting is enabled for all :)
You're the management committee. So manage. If a member has a complaint then discuss it formally, fairly and openly at a committee meeting and decide the matter, then publish the decision in the minutes, and if the accusation is serious enough call an EGM to decide it. You're a customer service organisation, you need to start treating your members with respect as customers. Sometimes customers can be extremely unreasonable, but that doesn't make them idiots, just unreasonable customers.
But in the week after an AGM, which is an open forum where we invite anything to be discussed an dpolicy for the year is decided, a member can't surely expect any respect if they then bring up issues which they failed to mention at that AGM, even when invited beforehand to put down anything they liked on the agenda, can they?