This is really good advice, imo, and has pretty much been my approach for the last 5 years.
I am often told of the purchase too late to do anything anyway and am often told of how these purchases did not meet the reservation expectations. Anymore I just offer the advice of making the reservation asap.
Bill
There is only a 10 day recession period. If it's past 10 days after purchase, then there's no reason to say anything about the resale market. That being said, the resale market is, IMO, the best way to purchase dvc UNLESS you want to stay primarily and only at disneys newest timeshare location, the Polynesian.
They probably purchased appx 150pts, which is enough for a week at their home resort, the Polynesian, depending on the season (give or take a few days). It's a wonderful resort, with rooms retailing at appx $500/night on average... So if they plan on going to DW regularly, it's a decent investment. If they were to sell their timeshare right now, immediately after buying their dvc, they would likely only lose 25% of their purchase price. This is assuming they bought at the Polynesian in Orlando, verses aulani in Hawaii.
At the end of the day, they didn't make a huge mistake-- as timeshares go. They bought a timeshare that tends to (historically) retain a good portion of their value. Some of the dvc properties have actually increased in value over time. Maybe you can take vacations with them and see how fun and nice a dvc property is!!