No pics - this was years ago - but the worst/dirtiest Mac I ever encountered was a Mac Plus used by a heavy smoker. If you've ever been into a house of such a person, you'll notice the walls are orange, greasy to the touch and should this person ever move or die, the entire plasterwork of the house would need to be replaced
Anyhow, this Mac Plus had the same greasy/orange tint as the walls, and the dust inside had solidified to a thick black ooze that I simply could not remove with any amount of heat/vinegar/soap and water. The dust ooze was impregnated with moisture, and wiping it back revealed it corroded everything it was on. It was disgusting, frankly a health concern, and the Mac Plus was ... removed from the premises, sorry to say.
Just remembered another one - an early Intel iMac - found on the street - looked fine externally, didn't start up. Cracked it open, wondered what all the little white pieces of sand inside were behind the LCD - pulled back some more - and was met with the biggest ant infestation I've ever seen. They came out angry, real angry - thousands of the little buggers. The "white sand" was ant larvae. I honestly had to run it outside into the street and dump it on the nature strip until the next waste collection! Funny thing was I didn't touch it for weeks after I found it, it sat in my garage awaiting attention, and I never saw one ant come out of it.
Another one! I used to visit a chap that was a classic hoarder, you had to push your feet through rubbish indoors, the entire house was blacked out and had been so for decades. However - there was this Colour Classic in the corner that was utterly pristine, nil yellowing - never touched, and like any hoarder, no attempts from me to kindly take it home were successful. I drove past the person's house recently and see he has moved (actually, no, 99% certainty he died), and that Colour Classic would have made it to the bin.
JB