BCastle is right, you want to keep your bigger and smaller roots together, otherwise you will get normal price for the big roots and find it harder to sell the smaller ones.
Only time I would separate is if I had a man root, or a few man roots. Those alone, if very distinctive, can fetch a good price by themselves.
If in doubt, you can always ask your buying all these questions. Each dealer is different and may prefer different type, size, age, etc roots so it is always good to sit down and talk with your buyer to find out exactly what they want and expect. Just taking a bag of ginseng to a local dealer and taking what they offer and walking away is never a good idea. Take the time to sit and talk to them. The man I deal with I call him at least once a week to check on prices, and he will talk for an hour if I let him. He has also gave me some very good advice for the season as well.