Buying is a good option as well, as you can buy a point for one cent. Since there are awards that include air miles and hotel stays, and the air miles are added onto the award stays at one point per mile, you are esentally getting airline miles for one point per marriot point.

I value airline miles between 1.1 cent to 2.5 cents and higher, depending on how they are used (BC upgrades and BC seats the most valueable to me). Buying at 1 cent is a no brainer for me.

Also, Marriott will let you buy more than 10% if you're short (up to 20%, if you're nice).

I've bought points, many, many times. Many.

Billy