Marriott ROFR, does the buyer lose anything?

If I purchase points or a legacy Marriott week from someone other than Marriott, they have ROFR. Not sure what exercise rates are these days for points, but, if they did exercise it, am I as the buyer out any money at that point in a typical transaction? Not sure of the sequence of events and what money may have been paid already. How can I protect myself from losing money in this manner if I am out?