I know that after I change my oil & filter, it's hard to read the level on the dipstick. I have to turn it so the light reflects off it just so - before I can read it. Dirty oil is easy to read. Some folks here brush the end of the dipstick with steel wool or sandpaper to make it easier to read.

Another way to check that things were done, is to put torque seal on the bolts that need to be removed in order to properly accomplish the task. For those that don't know, torque seal is a tamper proof indicator paste that comes in a tube. You put it on a nut or bolt after torquing; and if the bolt is moved, the torque seal flakes off. So, if the job isn't done the bolts should look untouched. It comes in different colors and available on-line or at some parts stores. Widely used in the aircraft industry.