Sorry for the delayed response. The GT3100 is a good machine. No differential lock, but its not something you use all the time anyways. Looks like it has a busted headlight, common issue, nothing to cry about. That mower has the consumer grade deck on it, which kinda blows. I think they are 46" or something, but the problem is that they are made of thinner steel and they use regular scalp wheels instead of rollers- it's not a floating deck.
My bigger concern with that machine is all the grass caked up around the deck. That grass holds moisture and it will rot out the metal underneath. Also if it is any indication of the rest of the mower, all the cooling fins are likely caked up too which can cause the engine and hydraulic pump to run hot. I wouldn't immediately shy away from it, but I would want to thoroughly inspect the entire machine- check under the deck, pull the side covers off the engine, take a look at the hydraulic system for leaks, etc. If it checks out, $750 isn't a bad price. A quick hit with a pressure washer and it might look almost new. But if I were given the choice between that tractor for $750 or a brand new tractor from Home Depot or Lowes for $1500+, I'd take that GT3100 hands down, no question. The 3000 series isn't a box store tractor. Some of them were close to $10k when they were new.
