If your ES is an 02, 03 or 04, then the air box is a little harder to get into.
Besides the two bolts, the small bracket holding a valve on the back side or the cover has to be removed so that the top cover can move up freely. They probably did the two bolts and could move the cover enough to get at the filter and called it quits. In addition, they may not have had the filter element in stock. I'm not surprised as the Denso filter has a different construction than most aftermarket Penzoil/Fram/STP filters.
I do all my own routine service, but I also have a garage packed with most tools needed to do the minor repairs from oil changes to brake replacement to pulling a motor out.
Most of the routine items are fluid replacements which are a piece of cake once you have done it one time. There are plenty of threads here that give step by step instuctions for the easy stuff.
The hardest part is the proper disposal of the old fluids.
Word to the wise though, if you choose to go somewhere else than the dealer, keep all your paperwork. Non-dealer service centers will not be able to log into the nationwide Lexus computer system so you will be responsible for keeping track of all service that is performed.
The service center (Toyota, independents, JiffyLube, etc......even some Lexus services centers) you choose is up to you. Some are very good and some are not that careful.
steviej