All I see is a basic 446 with a 48 deck. There is no rear PTO kit or a hitch of any kind that would add value. No wheel weights, front weight kit, tire chains or other attachments such as a Utility Blade or snowcaster. Opinions on value will often vary widely but while this one appears to be very clean and straight, the most I would pay is $1000.00 if the engine checks out with a leak down test and compression test.
The main problem here is that the clutch is not working properly and we don't know why. Therefore, the Seller is expecting you to assume the cost of putting his tractor back into working order. Suppose for a moment that he was selling an SUV that looked really nice but the transmission was not shifting gears properly. The onus is on him to make this tractor ready to go to work because he is asking a premium price for it. A new clutch from the dealer is $600.00 plus shipping and taxes.
It is not up to you to gamble on whether the old clutch can be repaired, especially at the asking price of $1500.00. Now if he was asking $500.00, then it would be worth the risk.
He's just fishing for a sucker and if I were you, I'd give it a pass.