There is a moment of possession in which other people do not know the good Samaritan's intent. The Samaritan takes momentary possession and responsibility for a purse or wallet that makes that Samaritan vulnerable.
There was a day when I would feel more comfortable in taking responsibility for someone's lost item. Unfortunately, today's society provides a greater opportunity for punishing the do-gooder than the satisfactory reward of action may provide.
This is a similar situation to the EMT thread from a couple days ago. A medical professional is legally bound to provide assistance for any public health emergency they may find themselves involved in. However, the opportunity for punishment for the EMT's good deed is too high for the medical professional to feel comfortable with accepting responsibility for any involvement.
It is that moment of responsibility that makes any good Samaritan vulnerable to punishment for their good deed.