It amazes me in this day and age that people are quite happy to ask a random stranger to watch their possessions. I personally don't like it and certainly would never ever ask someone random to watch my stuff. If I'm somewhere and someone asks me to watch their possessions i usually make some excuse like oh I'm sorry I'm leaving in a minute or just plain say no I'm not happy doing so.
On one instance a lady asked me to look after her dog whilst she went into a shop, i said I'd really rather not and she got really weird with me. I ended up saying, you don't know me, whilst i love animals i would really rather not have the responsibility of watching your dog, what if it were to get loose or worse still bite someone? I was also concerned that was this person going to abandon the dog her insistence that she wanted me to watch it raised my suspicion that this was a possibility.
In the end i watched her tie it up and walk off into a shopping centre, i did actually feel a responsibility to the dog not her to watch to make sure she came back to collect it. Which after about half an hour she did!
But when it comes down to watching people's stuff then no i don't do it.