Bechoros 4:6-7

Bechoros 4:6

If a person takes payment for serving as a judge, his rulings are void. If one takes payment for testifying, his testimonies are invalid. If one accepts payment for sprinkling the water of the parah adumah (red heifer) or for mixing the ashes and water, then his water is considered to be cave water and his ashes are considered to be fireplace ashes (i.e., ineffective). If any of the people providing these services was a kohein and the one who contracted his services rendered him ritually unclean and unable to eat terumah, he must provide him with food, drink and anointing oil. If the one performing the service was elderly, the client must transport him on a donkey and pay him as one would pay a laborer.

Bechoros 4:7

If a kohein is suspected of blemishing firstborns, one may not buy venison or untanned hides from him (even though deer are not subject to the law of firstborn animals, because he might be substituting calves). Rabbi Eliezer says that one may buy the hides of females from him. Similarly, one may not purchase washed or unwashed wool from him, but one may purchase spun wool and felt (which is pressed wool).