Hey,
It's best to send the customer a link to your google maps listing asking them to put the review there themselfs. As you pointed out above if you had 10 reviews all from the same google ID and IP address it will get flagged by google.
The below link is for google guidelines on reviews. One of the points they have is impersonation.
- Impersonation: Don’t post reviews on behalf of others or misrepresent your identity or connection with the place you’re reviewing.
