John Gill Commentary Leviticus 27:12

"and the priest shall value it, whether it be good or bad: as thou the priest valuest it, so shall it be." — Leviticus 27:12 (ASV)

And the priest shall value it, whether it be good or bad
Put a price upon it according to its worth, as it shall appear to him:

as you value it, [who are] the priest, so shall it be ;
that shall be the price at which it shall be sold, not to the owner or devoter of it, for he must give more, as appears from (Leviticus 27:13) ; but, as Jarchi observes, to all other men who come to purchase it.