I think I'm in the same boat as the OP...
There are a few mills around here that have what they call an open yard, they take everything, any way you can get it to em, legal or not... (stay legal please...) they may not pay the best but they will almost always buy. I've taken anywhere from 2 logs on a borrowed car trailer, to full log loads, they buy it all.
Call the mills in your area find out what they buy, if they are buying, what they want for lengths, diameters, plus wastage/snipe etc.
trim the knots down to nothing, keep the logs as clean as possible (mud rocks etc), give the mills quality logs all the time and they will learn to like you, give em junk, they may eventually stop buying from you.
Remember the mill holds the purse strings, you bow to them (yeah its sucks I know...) they pay what they feel the log is worth, not what you feel your owed...
Keep your costs low, if the skidder doesn't need to be running shut it off, make as few trips back and forth to the site as possible, don't run things hard, you'll do better running light and fast then heavy and slow. Plus you won't break down as often.
Be honest with the landowner and their neighbors... the dishonest gypo doesn't get work for long. Most the work you will get will be word of mouth, do a good job and they will tell their friends and family all about how you came through for em, cheat em and they may even call the police...
Good luck, its a tough little world and allot of very hard work, but worth it when it works...