The airlines do have a good safety valve: offering people increasing amounts of money (not vouchers, but actual currency) until they get enough passengers who prefer the money to traveling on that flight. They just don't want to use it.
Oversell is sometimes known with high confidence at checkin-close (1 hour prior to departure) or even before, due to the fact that oversell thresholds can change throughout the booking curve.
Airlines don't have a current solution to rebalance/correct loads prior to the gate auction.