You Will Get Nowhere By Doing What Everybody Else Is Doing.

Here is a simple and quick answer, but value is not determined by the number of words.

Whatever system you do, don't do it immediately. Send a letter to the guest one month after their stay. When people get back home, they are too tired to pay attention. On checkin, their is simply too much going on.

So, send a letter with the points earned and say, "We would like to double the offer, please send the enclosed link to a friend or family member and they will get the same amount
of points listed on this letter."

Good Luck,
Michael Von Irvin