I'm not saying it didn't happen, but it's never happened too me. I work alone, i build a few engines a yr. and if i get a visitor to my shop (which is rare, i live in a one dog town) i simply cover up the engine until they leave. I have been building for 50 yrs. and that's alway been my procedure. I don't distrust the visitor i just don't need the distraction when i'm putting together a $5,000.00/$10,000.00 motor.
JMO
Zip.