Before renting a boat to a stranger, it is important to take steps to protect oneself. The first step is to get adequate insurance that covers personal liability, as well as theft, loss or damage caused by someone renting the boat. Strict policies on usage and cleaning standards help in maintaining the boat. Security deposits are a good idea as well.
No. It is not wise to trust someone you don't know since you don't know how they behave or if they have morals. If you trust them without knowing them, they could easily steal your boat away from you. It would be better to get to know the person first before you put your trust in them.
Driving a boat is a lot harder than driving a car and it takes some specialized skills depending on the size of the boat. I think renting boats is a terrible idea and places a lot of liability on the owner. Most people renting boats would do so in order to have parties which I think is a recipe for disaster.
You can not trust a stranger with your boat. You boat can be trashed by a stranger it may be hard to come back on the person that did the damage. I would not trust a stranger with my property, boats are a big investment and you have got to protect them.