You could buy that machine brand new (minus GPU) from somewhere like PCSpecialist for around £900, and then pick up the GPU new from elsewhere (e.g. Amazon) for around £275. Second hand hardware should not be that expensive...
Yeah, no one is going to buy that. I have almost the exact same computer, with a few better parts, more expensive case and more expensive fans. Bought it brand new and it cost me almost $1200 less than what you're asking, and this was something like 18 months ago.
If you're having trouble selling it as a whole then maybe you'd have better luck selling each part individually. As others have said I believe the price is too high.
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Good luck.