This is another short story that I read when I was a kid. I think that I was in elementary school at the time, so it was likely written before 1989, and absolutely no later than 1993.
I read it in English, in the USA (Minnesota). It was possibly in a school library book, but I think it's more likely that it came from the scholastic book club.
This was a very short story, likely in a collection of short stories rather than from a stand-alone source, probably a collection of creepy stories for kids.
The basic plot was that a traveling carnival showman/con man-type (possibly named "Crispin") had a robot show that he charged a fee for people to attend - the robot did tricks and such. The gimmick was that, at the end of the show, he'd open up the robot to reveal that it was all wires and gears inside. The audience was said to assume that there was a Little Person or child inside, wearing the suit like a costume, as this took place at a time when high-tech robotics weren't real yet. Revealing the robot's innards impressed the audience with how high-tech the "robot" actually was.
The twist was that, later that night, he'd take the robot back to his campsite (or possibly a trailer?), and fully open up the robot to reveal a tiny cabin inside, filled with levers and gears, and an actual dwarf manning the controls. Not a Little Person or "midget" (to use the outdated term), but an actual non-human magical Dwarf (or Brownie or Elf or something similar - I don't recall whether it was ever specified as to what sort of being it was).
It was clear that the Dwarf was a prisoner being held captive by the showman.
The man put the dwarf in a cage, basically a big box with air holes on it, then threw his coat over the cage and left (to get dinner or drinks or something, I think).
When he returned, he heard the dwarf complaining, begging, "Please, more air! More air! More air!", and he started to go on a cruel (possibly drunken) rant.
"You always want something, don't you? 'More food', 'more water', now 'more air'? You're never happy!! You do nothing but complain!"
Then, the voice of the dwarf started to grow more faint - "More air... please... more air...", and the man realized that he'd thrown his coat over the air holes on the dwarf's box. By the time he reached the box to uncover the air holes, the dwarf had suffocated and died.
I remember that part of the story pretty clearly - those quotes aren't exact, but I think they're fairly close. However, I do not remember the ending very well.
I think that the man then locked the body of the dwarf in his robot suit and dumped it in a lake, and somehow the ghost of the dwarf piloted the suit to haunt the man for revenge, but I can't remember the details of that.
I'd love to track this down, and I think it's possible that some of the other stories I've asked about ID-ing were in the same short story collection that this one is from.
Hose on Pearl St, about a giant man who kills kids and keeps their souls locked in the house. I think Supernatural even had an episode very similar plot!