users do make some human error mistakes and the game try to protect against it (i.e. "confirmation" button before firing a player)
In this case users might want to self bid after something happened that they couldn't predict or control (not human error) - such as other player getting inj and making the sell not worth while.
Other case might be that the player being sold got inj and his price is lower then what manager wanted to pay.
Users pay for self bidding. taxes are payed and % drop to ~79% again.
"Did you miss me??? - "With every bullet so far..." Al Bundy