Asking for advice should be your default method early in your customer discovery process. You will have better luck gaining access. People like being asked (it makes them feel important). Steve Blank used to call people up and say something like, “My name is Steve and [dropped name] told me you were one of the smartest people in the industry and you had really valuable advice to offer. I’m not trying to sell you anything, but was hoping to get 20 minutes of your time.”