exept ur forgetting that just because its 2 years old doesnt mean its worthless the parts are worth quite a bit more and also the computer is in great condition. also by ur logic with it being 2 years old i can sell a gtx 1080ti system for 300 right
The parts are worth more new, and just that parts.
You will get more than 300 out of it parting it out, but the typical buyer will see a PC used for 2 years and not want to pay anywhere near retail price for components.
To answer the second half, 1080Tis sell for 450-550 used.
Systems with 1080Tis in them sell for as low as 800 depending on specs.