The first time I chartered almost 30 years ago at the Moorings in BVI, I filled out an experience profile that showed I had worked my way up from sailing dinghies to belonging to a sailing club where i sailed 30-35' cruisers, all day sailing. That got me in the door and I am sure that they made another evaluation when I got there and must have passed.
Today at least in the US I don't know of specific certifications required, only enough experience. Tell them you sailed your friend's boat by yourself and you will probably be ok. At worst if you fail the in person evaluation they will require you to use a captain for he first day or two.
Frankly, I believe it is all about how confident you present yourself not necessarily specific experience.