Related for Chagigah 51:17

If tax collectors entered a house and wrote on the outside [that] everything that is in the house is [ritually] pure, they are believed as to the purity of [articles involved in] the purification rite [of the red heifer], but they are not believed about the purity of Terumah, and in Jerusalem they are believed as to the purity of all the consecrated utensils but not about Terumah, and during the season of the pilgrimmage festival, [they are even believed] about Terumah. One who buys utensils from am ha'aretz skilled craftspersons, and one who sells utensils to am ha'aretz skilled craftspersons are believed about the purity of [articles involved in] the purification rite, but are not believed about the purity of Terumah.