The fuel will definitely be bad. The battery will probably be needing replacing. The oil will be fine but should be changed. The mice might have made a nest and maybe chewed the wires. There could be other maladies due to dormancy. You might run into more expense than what you'd get back. Best to get estimates.
I would think that the best case for you is to say the tractor sat for 6-7 years and sell it as "ran last time" to a mechanically inclined soul who will get it running again.
We could hear from the gloating buyer maybe needing some advice in repair.
