That's an interesting question. Marriott has many different partners that offer points that can be redeemed as Marriott cheques. I have redeemed them in denominations of $50 and $100 and only use them to pay the balance at check-out. Marriott cheques have an expiration date and the T&C specifically states that change/credit will not be issued.
I found a link under https://www.marriott.com/rewards/use-points.mi
The direct link for gold members is at https://www.marriott.com/rewards/usepoints/eliteRewards.mi?segmentId=elite.gold