These chains include Travelodge, Days Inn, Howard Johnson, Super 8, and several others. They are all owned by the parent company Cendant, and you can see them listed at TripRewards.com .
So, I do research beforehand on other various booking sites to see if I can find a cheaper rate elsewhere. Sometimes I can't, but often I can. Then I book the room, which is cancellable, via the chain web site (like Travelodge.com or whatever). Then almost instantly, I submit a claim using the Claim Form on that web site. So far, I've gotten about 12 free rooms this way. The hotel clerks have treated me fine (some stays are in the future so we'll see). The hotel rooms have been fine too. I know that some hotels in these chains might not be okay, but you can research with TripAdvisor.com also. The pitfall is that the two rooms must be identical on the two web sites. So if one room is 2 Doubles, Non-Smoking, finding a room that is 2 Queens, Non-Smoking is probably not a match (but it would be worth a try).
I also only book one night. You can't get two consecutive free nights.
(by willtravel, guideforeurope.com)