Can you watch my stuff?

Have you ever been just sitting down, minding your own business, when all of a sudden a complete stranger walks up to you and asks you to watch your stuff while they go off and do a quick errand? This practice has always bothered me for many reasons, and now I have a sudden urge to turn this seemingly normal practice into a project.

First of all, I really can't stand it when complete strangers ask me to do this. There are so many problems that can arise! My main fear about this is that if I agree to watch someones stuff, they could take forever to get back and get their stuff. What if you want to leave and they still haven't come back yet? It just means that you're stuck there until they come back, so you gotta force yourself to look busy when in reality you just want to leave! And you gotta act really nice about it also when the person comes back because its just common courtesy. You can't be a super villian and ruin that persons day just because they ruined a small part of yours.

This really isn't the main thing that bothers me about looking after a persons stuff though. I get super bothered if someone other than the person gets their stuff. For example, lets say a young male asks you to watch their backpack. He goes away, and a little while later, a old female comes up and starts searching the backpack. I seriously don't like any of the next steps in this situation. Asking the person is very awkward to do, especially if the person seems as if they know what they're looking for! you can't assume that they're a friend, but you also can't assume that the person is an enemy! Its a lose lose situation!

Also, what if it really is someone trying to steal the person backpack? What are you going to do about it? I'm sure as hell not going to risk my well-being over some random persons belongings. You can only hope that the person taking the backpack is someone that knows the original owner, and if not, then you're in deep shit with the person that set you in charge of their belongings.

This all makes me wonder, to what extent will people go to protect another persons belongings? One of these days, I'm going to perform a experiment. I'm going to have a friend ask a stranger to watch their stuff, and after a little while I'm going to come up and start searching through their stuff. The goal of this is to see how certain people would react in this situation. What would you do? Would you ask me what I was doing or who I am, or would you completely ignore me and assume that I'm just a friend of the original owner? Would you get into a fight with me over the belongings of another person?