Folks, being married to a FA I can tell you this does not happen often. GAs know that favors can cost them their job. Upgrades to non revs are part of a written record and have to be accounted for just as revenue upgrades do. Non Rev seats in premium cabins do happen if there is no one waiting or they can be put in F even if business is full and upgrades are waiting there from coach.. It is up to the discretion of the agent working the flight.