They can do it without having an account and/or logging in?
This is where I was running into some issues, people not having a yelp account and even if they made one if they only had 1 or 2 reviews it was hidden as it was assumed to be fake I guess.
It's cool that people can review without signing up/in if the reviews stick.
The letter that I had was closer to- if there are any issues please let us know, if not please consider giving us a review. I had my wife send them out to every customer for a while. A podcast I listen to emphasizes treating everyone like they are going to review you on social media (The MFCEO Project), this put me in that mindset more. We live in a very connected World now.
"try to become not a man of success, but try rather to become a man of value."