I really have no objection to players being able to "market" themselves in college. The issue for me is how this could be potentially abused. If a player autograph is worth "X" on the free market and the player manages to get "X" so be it.
The concern would be say an unscrupulous booster who tells recruits that every freshman gets a signing day after they enroll and they are paid "10 times X" per autograph, all subsidized by booster(s). This isn't a player marketing themselves on the free market but rather artificial inducements for recruits who enroll. I'm sure creative people will come up with other ways to scam the system.
Hopefully between the states and the NCAA/athletic directors they can come up with a way to make this happen that doesn't allow schools with lots of big money boosters to scam and skew the system. Still, I'm pretty sure this will skew recruiting in the direction of schools in states with large populations with plenty of fans willing to pay to get something from the player. Wisconsin, Minnesota, Nebraska, BYU might have more problems enticing high level recruits than say schools in Cali, Texas, FLorida and Ohio. . . . not that it's not sort of already that way.