It's a very good mower, and if it has the Kubota diesel engine it is a Great machine.
1700+ hours is nothing on a Kubota diesel, That is about 120 hrs a year... check the deck wheels and blade spindles for ware, if it has been serviced everything should be good.
It sounds like you are dealing with the actual owner/operator, so you should get a better idea of it's past history.
As to price & condition you can compare that one to these:
http://www.tractorhouse.com/list/list.aspx?ETID=1&Manu=GRASSHOPPER&MDLGrp=725
I would feel better with the diesel engine.... :smile:KennyV