I spoke to my agent last night (it got loud ), she told me that she will contact the other agent and demand an apology. I told her that was not satisfactory,and asked if the other agents supervisor knew about this incident. I told her she is responsible for making it plain that there is a hands off policy or I take my house off the market.

It sounds like the people looking at my house had some kids with them and just left them run loose (sounds like Guitar Center or Best Buy doesn't it?). I see no reason that I should have to move my gear, I need my gear handy because I get around a bit. The other firm is a large national company, if I don't get satisfaction I will contact their home office to see if that motivates them.

Yes.... but in the end when something you care about is damaged, that is the end.
No lawsuit, apologies or restitution will bring that instrument back.

Seriously we rented our house on Block Island for many years and we learned the hard way that no matter what the contract or the assurances from the realtor and their agent, valuables get broken or worse end up missing.

Just for your own piece of mind put the instruments away locked up out of sight....
The last point is very critical, you cannot know who is looking at your house.
It has happened that potential buyers are actually scoping out a house for burglary and have zero interest in purchasing, it's a reconaissance trip to assess the interior and it's potential...

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"C'est parti mon Kiki "

This just happened about 2 months ago to some people that I know back home in SC. They have their house on the market, somebody came in with a realtor to look at it, he casually unlocked a door to an upstairs balcony, and then broke in later that night. Of course, he didn't count on them being home when he decided to break in. The .357 Magnum scared him pretty good. Too bad he didn't get hit.