Word / phrase: To vouch for someone

What does it mean? This phrase is used to say that someone or a company you know is honest and true. Someone you can trust.

Is it positive or negative? It's positive and shows a person or company in a good light.

When do you use it? It is used often when someone is looking for a certain person to do something. A recommendation.

Example 1: The guy who came to fix my toilet was really good. I can vouch for him. 
Example 2: I know her, but I don't know if she is any good at is job, so I can't vouch for her.
Example 3: I'm looking for a native English speaker and a friend of mine vouched for you, so I'm interested in having Skype or Zoom lessons. 

Question: Would your friends vouch for you if someone was looking for someone who is hard-working?