Google encourages you do to is to create a review friendly link. Following steps other than these could lead to reviews being removed or even being penalized in search results.
1. Go here https://developers.google.com/my-business/content/faq#associate_locations_using_placeid_1
2. Type in your business name and then select it from the drop-down.
3. Copy and paste the Placed ID into the end of this:
Then have your client use this link above to send to customers and the review box will automatically open AND it’s safe to use.