replace oil pan gasket

Id like to know how the gasket was replaced without removing the bolts holding the pan on. Upon doing an oil change I noticed the pan bolts were covered with the same amount of years worth of oil and dirt build build-up as the bolts on the transmission pan which had never been removed. The work was obviously never done. Charged for. Just not done. Their comeback was "Well, that stuff builds up pretty fast." Yeah, right.