this thing is common, specially to toyota service center. they would try to sell parts to you so that they can earn a commission from it. now if you would be a real pain to them by asking why would they replace it and show you on the maintenance manual of your car that it really needs a replacement at that time or mileage or ask them about the manhours that they have consumed, then they would back down and would be honest with you about the true cost of your service