Which preposition to use with valuers

at Occurrences 1%

Arthur Biddell was a prosperous farmer and valuer at Playford near Ipswich.

by Occurrences 1%

Railway companies were especially plundered in the exorbitant valuation of lands, and therefore an advocate who could check the valuers by cross-examination was sought after.

for Occurrences 1%

Sometimes I led a witness who was an expert valuer for a claimant to such a gross exaggeration of the value of a business as to stamp the claim with fraud, and so destroy his evidence altogether.

Which preposition to use with  valuers