Meh. I prefer a smaller device as I work in and around a lot of trees. A 7 footer would jack me up pronto. It's also hard to sell such a big thing should you have to. Anyway, I agree that a rust hole means it has been sitting in the weather for a long long time.
As you probably already know, the working parts of a rotary cutter are usually in fine order. It's the deck and blades that go. If you go look at this monster, be sure to get a good look underneath at the pan, the blades and the hardware. If you find that you have to put new blades on it and you need to demolish the nuts and bolts to do that, your bargain cutter just became no bargain. Another thing to consider is whether your loader raises high enough to pick it up for maintenance.