Ask your client. Your client has full ownership of the game and can do what they want with it unless you stated otherwise on your gig page.
EDIT: Funny that the correct answer didn’t get marked as the solution. 😂
I am pretty certain that a buyer will be asked to leave private feedback about 24 hours after the order has been marked as complete. So a buyer should be able to leave private feedback without leaving a public review. However, I cannot be 100% sure as I always leave a review for sellers.
I purchased something a few days ago, and like @krheateI was only asked to leave private feedback after completing my order (I left a review). I was asked to leave private feedback the following day.
Oh, and since the buyer is asked to leave private feedback after completing the order, a buyer could perhaps be tempted to leave negative private feedback as revenge for a seller leaving a less than 5-star review for the buyer. For this reason, it might be beneficial for a seller to only leave 5-star reviews for buyers unless they are absolutely sure that the buyer is going to be leaving a negative review.
I don't like the way this is set up, but that's how it is.