Being overly suspicious of everyone is a terrible way to live. Maintenance should have the autonomy to do as they did here - and security correctly followed up. The right response should only be technical imo. A meeting room should not lead to this level of network access.
> Maintenance should have the autonomy to do as they did
Really? We're talking about letting strangers in through the literal back door.
A better approach is to train everyone to be polite and helpfully walk the person to reception, who can arrange access.