This thread has made me quite paranoid.
I've just bought my 1st new guitar in ~20 years which is old & unmolested, except for the tuners being swapped out. I have replaced them with more period correct tuners & stuck the others up on the bay. I specified the guitar they had just come off, which is reasonably valuable, in the ad & have immediately got a response from someone who wants to pick up. Thanks to this thread I'm now thinking he's going to work out when I'm not around & pinch the guitar.
Cheers for all the horror stories.