The reason the automobile mechanic phones you regarding a $300 part is that, if they perform the work WITHOUT consent, the customer does not have to pay for it. That's why dealership Service Advisors have you sign the Repair Order before they begin work on the vehicle.
LAMEs on the other hand, have perhaps not encountered this phenomenon and I have associates who have experienced the LAME quoting a job to get the work, then when it's time to pick up the bird, the quote has blown out. (By several THOUSANDS OF DOLLARS)It's the same principal, but the dealers have been burnt doing this, so they get approval... It's hard to stand up to an expert working on your bird though...