The answer is you draft on your grade and you have to trust your board. But you also have to take into account value. If you think or know that other teams have a lower grade on the player, you wait to take him until you think other teams will take him with their next pick before your pick.
This isn't unique to RBs. But the difference is that there are some positions like RB, Guard, LB, and Safety where you can usually get better value after the 1st round. So, to maximize value, it makes sense to trade down if you can get good value for the trade down. If you can't, you take the player.
But, I guess the counter question to you is if you have a pure Guard, can't move to Tackle and can only play Guard, rated at #9 do you take him?
My answer is the same, you look to trade down for good value.
But, it really all depends on how you grade the player. If you think Jeanty, or any other back, is the next LT, Faulk, Sanders, etc., you take him at #9.