What I am looking for is the guys like Ryan Grant of last year. He should have been sold during the offseason (even after the draft since GB didn't really take a RB that would challenge him). On the "buy low" side, I would say someone like Calvin Johnson, Roddy White, or Chris Johnson. Even a Thomas Jones (who could have been had for a song and was very valuable in start 3 RB leagues).
After the 2003 season, I had Julius Jones and Kevin Jones on one of my dynasty rosters. Both of those guys are near worthless in FF leagues right now, but that wasn't the case at the time. They were consensus top 3-4 rookie picks who had shown serious flashes of talent during their rookie seasons. Both guys were ranked as consensus top 10 dynasty RBs. Should I have sold high? Of course, but it's a lot tougher to make that call when you're the one sitting there with two 22 year old RBs who look like future stars. You tend to want to keep guys like that. How was I to know that they had both already peaked?Knowing when to buy and sell is a delicate art. On some level it's just a judgment call. I think Eddie Royal is going to be a useful FF player for a long time. Why? Because he was a high pick, he has freakish combine numbers, he had rare production for a rookie WR, and he passes the eyeball test with flying colors. I'd feel comfortable acquiring him in a dynasty league at his current cost.
I'm less certain about someone like Matt Forte. He had a great FF season, but there are reasons to doubt him. Most of his production was the result of a huge workload and a slightly skewed (IMO) number of TDs. He wasn't a workout warrior like Eddie Royal (he doesn't have rare physical gifts) and, more importantly, he was held under 4.0 YPC in 10 of his 16 games last season. He didn't play exceptionally well. He just put up exceptional FF numbers. I think it's
possible that he'll become a consistent top 10 performer, but I'm not convinced that it's
probable. Given that Forte will certainly be valued as a consensus top 10 RB this offseason, he's an example of someone I would try to sell.
Ultimately, there's no way to know for sure. It's just a judgment call. You have to weigh the variables and make a decision. The quality of your decisions will determine the fate of your team.