Or HaChaim on Deuteronomy 16:21/אור החיים על דברים ט״ז:כ״א

1 לא תטע לך אשרה, "Do not plant for yourself a 'sacred' tree, etc." Our sages in Sanhedrin 7 have said that if one appoints an unsuitable judge this is similar to violating the commandment of this verse. According to the sages then the word לך in our verse means that the appointment of an unfit judge is objectionable only if it was made deliberately in order for those who appointed him to benefit from perversion of justice. If, however, a judge was appointed in all innnocence, and it turned out that this judge was not competent, no sin accrues to those who appointed him. The people who appointed said judge would certainly not be comparable to people who plant an אשרה.