I change my own oil simply because I trust my own work more than others and that last little bit to drain out usually contains what needs to drain out the most. One thing I did not read was the problem Ford had (I assume other brands also) with dip sticks being marked wrong. Every professional mechanic I have talked to will also was recommend relying on the owners manuel or shop book for liquid amounts as oil pans, etc. vary based on end use and dip sticks may not be matched correctly to the oil pan.