I’ve done the valve stem core removal in a younger day. I just threw the cores in the grass; I didn’t think they would find them.
Another trick is if they don’t have a locking gas cap, you open the cap. Then take a half of a five-pound bag of sugar, pour some around the cap, dump the rest of the bag on the ground under the gas cap, and leave. There isn’t actually any sugar in their gas tank.
But they don’t know that.
A trick from when I was very young: There was an ongoing ‘feud’ between my older brother and this jerk in the neighborhood. Mr. Jerk had a very nice clean ride: ‘56 Chevy, (if memory serves). My brother put a ping pong ball in his gas tank. Causes no issues until the tank is low. Kills the engine, engine restarts, then dies again as the ball blocks the suction to the fuel line. Mr. Jerk went nuts trying to figure it out. He eventually sold the car to a friend of my brother, who knew what the problem was.
So..
It WAS YOU!