My impression is this has had a bandaid paint job done. Some things that make me believe this: tail wheel has been painted. Places where paint is thin, not sure if rust is bleeding through or if repair work has been done and primer is poorly covered with red. Places where paint has chipped away or were just missed in painting. Lots of pitting in the metal that has been painted over. Thump on the metal, not hard enough to dent it, but enough that if it is painted rust it will flake the paint.
With that said, check out all mechanical points on the brush cutter: spin the PTO by hand, is there play?, are the U joints sloppy?, are the shafts on the gear box sloppy?, what shape are the seals in, signs of leaks?, is there gear oil in the gear box?, what does it look like—milky?, do the blades spin freely—they should be free to spin from the gear box spinning should they hit a stump or rock?
I am sure others have more points to address, but personally I would rather not have the bandaid to truly see its condition. If the seller does not want to you look it over closely—leave it behind in a hurry!