Found a used F687 with a 54" 7 iron deck. 2 years old. Out of warranty. Has 1 huge, wide single wheel in the back (JD website shows dual wheels...what is this?) Has a 23 hp Kohler twin. 130 hours on the machine. Looks very clean. He wants $6800.00 What is a reasonable price? Owner is getting out of the business, he says (no time...newborn baby), I assume it was a side business . Anything on this machine to double inspect? Any known problems? Anything not so great, other than somewhat slow speed?