OK, so how do we know that the landers and rovers are there?
* The astronauts recorded thousands of still images and movies of the descent, the exploration, and their departure - a historical record of the events.
* The moon rocks brought back by the astronauts have been examined by scientists the world over and are unquestionably of lunar origin.
* The ALSEP science packages put on the surface by the astronauts radioed back significant amounts of data.
* The seismometers recorded "moonquakes", and when the astronauts returned to the Command Module they jettisoned the landers and crashed them into the moon and the seismometers recorded these events as well as the crashes of the Saturn IV B stages.
* The Apollo 11, 14 and 15 missions left behind "corner reflectors" which astronomers (e.g. McDonald Observatory, Texas) can use to measure the distance between the Earth and the Moon precisely, even today. This has been upgraded recently to the Apache Point Observatory Lunar Laser-ranging Operation. We now know the range from the Moon to Texas within one millimetre.