Another term for "lies and deceit" in Marcelo and the Real World could be "Sandoval and Holmes." Their lies are whoppers and cause a ton of suffering. And even though Marcelo knows this is very wrong, he learns to do a bit of lying himself. As soon as he learns how Vidromek (and therefore Arturo) hurt Ixtel, his black-and-white world turns gray right quick. To Marcelo, sustaining a lie feels like giving the hamster on the wheel of his brain a Red Bull and a triple espresso; it's not easy or comfortable. But he's willing to think fast if it means Ixtel can get a new face.
Marcelo understands that lying is wrong, but he's willing to lie to Arturo to the point that he jeopardizes the financial security of his whole family. That makes him a bit of a hypocrite.
Arturo and Holmes have become rich by lying, and the richer people become, the more they tend to cling to the habits that made them that way. The desire for wealth can cause people to abandon the truth.