lots of things to look at: I assume that it is the old style wobble box, not the oil bath type. This affects value, as oil bath is more desirable. Is it a 3" cutterbar or 1.5". 1.5" are more expensive to maintain and can give more problems. look at knife guards and see how much wear is on them. If much, replace them when you replace the cutterbar. look at the grain pan in the center, that front peice will wear out where the seam is, and it costs about $300 to replace it. look at the plastic bushings on the reel. If there is too much slack in them they may need replacement. look for cracks on the outside of the end pieces (sides) where the auger attaches. Check driveshafts and U-joints. Make sure plastic shields are in place. If header has poly skids, make sure all are still on. Check that header control linkage is intact. See if all the flex springs and runners are working. Make sure reel lift cylinders are not leaking. Check the auger drive sprokets, they seem to wear out pretty quick. Make sure it has the lockup straps bolted under it somewhere. About all I can think of.