There are a few people that do it in my area. Some of them just wait at the sale barn and haul smaller loads to local farms. There are also a couple people that make daily trips to the larger barns hauling everything (sheep, hogs, cattle, goats). The guy we usually get charges by weight, his charge is taken right out of the check we get from the salebarn. He usually has a good idea of what the market is going to do and will tell us to hold them another week or two, or give specific days where the slaughter plants aren't backed up.
I'm sure there are a lot of headaches, but that is how he makes a living. I think he has a 24 foot trailer, and makes a run everyday. Also he backloads feeders and cows back up sometimes.