If we go back to the original question-- do you think this happens a lot--I believe the answer is no. Consider that DVC has about 60,000 members. As far as a rental market goes, it is essentially non-existent except on the internet. You have a place on this site and a couple of other sites and e-bay to rent and thus if you look closely enough you can see about everything that is going on in the rental market. You will see a handful of people who seem to be in the business of renting, some others who appear to rent out some of their points mainly to cover dues and perhaps make a few bucks, and, for the most part, a dozen or two members at any given time trying to rent stays they have to give up because they cannot now go or members renting points because they cannot use them before they expire. In other words it looks like there is a very tiny rental market when you consider that there are 60,000 members.
Moreover, it is not the kind of market where someone can go into the business of renting and expect to make a lot of money. First there are limitations on the number of points anyone can buy (2,000 at one resort, 5,000 total) and thus rent. Second, the average rental rate of $10 a point is not reassuring to persons who would want to be in the business of renting--they have to pay high dollars for the points, they have to pay dues, they have to find customers, deal with the risk of market collapses like right after Sep 11, and expect other problems like customers who cancel, fail to pay, or expect you to be available 10 times a day for a phone call to talk about the reservation. Moreover, if they are in the "business" of renting (meaning they are essentially doing nothing but buying lots of points and then renting them all), they are required to remit the regular resort rental tax (11% for WDW area resorts) to the appropriate government authorities.
In other words, I do not look at it as something to get concerned about. The problem with surfing the internet is that many get to see the renting that is going on but don't consider that they are actually seeing ALL the renting that is going on and it isn't much. Members retain the right to rent. The "commercial venture" limitation in the documents really applies only to someone who actually does go into the business of renting with no intent of using any points himself. There may be some of those but not not enough to cause any real concern.