Leviticus 27:9

"And if it be a beast, whereof men offer an oblation to Jehovah, all that any man giveth of such unto Jehovah shall be holy. He shall not alter it, nor change it, a good for a bad, or a bad for a good: and if he shall at all change beast for beast, then both it and that for which it was changed shall be holy. And if it be any unclean beast, of which they do not offer an oblation unto Jehovah, then he shall set the beast before the priest; and the priest shall value it, whether it be good or bad: as thou the priest valuest it, so shall it be. But if he will indeed redeem it, then he shall add the fifth part thereof unto thy estimation."

Leviticus 27:9 forbade any substitutions. Once a beast was designated in a vow, the decision regarding the animal was irrevocable. In case a substitute was offered, the penalty required that both animals be forfeited. In the matter of unclean beasts (Leviticus 27:11), although these could not be sacrificed; "But they could be used by the priest, or sold for profit."[6] In case the giver wanted to redeem the unclean beast, he could do so by paying the estimated value plus twenty percent.

Leviticus 27:11 appears to forbid any haggling over price. Like the decisions of an umpire in a baseball game, the priest's evaluations were not subject to challenge. "As the priest valuest it, so shall it be!"