IF he bought a high demand unit at pre-construction prices, there is a small chance that Marriott will buy back the unit for at or close to what he paid. However, that is a big "if."
Marriott will act as a resale agent, but they have to want your week and have a market for it. Thus, except for a few very high demand weeks, there can be a wait list to get on the sales list for several years and, if you eventually move up to the top of the wait list, they will contact you to resell your unit. They charge a 40% commission of current selling prices.
On the resale market the value can fluctuate, depending upon the week in question. Very high demand weeks tend to resell for as high as about a third off current developer prices (Platinum ski weeks, Platinum Aruba weeks, Hawaii weeks with good views, some premium holiday weeks), while most sell in the 40-50% off range. Less desirable weeks sell for even a better discount and, with the economy being what it is, there have been some great resale prices lately with many passing ROFR.
Unless he really has a high demand week and bought really early on "we'll buy back for what you paid" is a dream.
