I am interested in purchasing a grain cart. I have noticed a few decent looking John Deere 500 carts. They are made by United Farm Tools for John Deere. A model 500 must not really hold 500 bushels? The last one I looked at didn't have any added side boards. Are they balanced well on the axle to provide some weight on the tractor but not an excessive amount? Besides the condition of the augers, tires, and gear box what should I be looking for? Looks like they sell for $3000 to $6000 on dealer lots. Seems like they are worth a lot less on online auctions. Thanks for any ideas/comments.