Depends on the instrument, I certainly don’t let audience members and fellow orchestral players who rush up to my harp to admire it (with their hands) get anywhere near it, I deflect their arm and hand away as they stretch out and likewise I tend to guard other players’ instruments after a concert when they are fetching their covers. People come up to it for a closer peek then turn around with a rucksack and back into it, whilst they gaze around the hall or cathedral! But a small instrument bought to share with pupils is okay, so long as it’s supervised and the harp isn’t pushed forwards and over.