If the rover sent back pictures that looked more like Earth, then they might get too many questions if they were really on Mars.

Agree, it is possible too.

I'm observing what happens in ham community, they began searching ways to receive transmissions from interplanetary missions and already have some progress - https://spaceweatherarchive.com/2021/02/16/ham-radio-signals-from-mars/ It is much more interesting and much more convinceable than making collages in photohsop.

PS: Nice Caddilac story, gives a clue how sheeple brain works.