Sounds like a deal to me. I got a good deal on a used 665 about 5 years ago. It's had minor issues, but nothing major. I've had no problem with parts availability.
Pros: price, easy to work on, built heavy, parts still available
Cons: loud, vibration at idle, fuel system is finicky
Things to check for based on my experience. I think most of this would apply to the 535:
* Fuel float had come off the rod and the fuel gauge wouldn't work.
* Check for clean fuel tank. Depending on previous owners care in re-fueling, the restrictive strainer in tank likes to stop up.
* I've had to replace all 3 injector lines because of rubbing and vibration. Tie wrap, bending lines and rubber isolators have fixed this.
* Several external bolts have backed off. Check all the bolts for loose fittings. Especially on the bottom where the 3 pt mounts.
* Had to weld new tabs onto the front grill. They were flimsy and had been taken off so much, they'd broken off.
* PTO clutch lever push button sticks and is hard to lube.
* Neutral safety switch on mine is going out. More and more I have to wiggle the lever to get it to start.
They're crude tractors, but overall, they're decent.
