[Ash]

As best I can tell. astronomical telescopes, either mirror or refractor, usually have substantial field curvature that is troublesome at typical photographic distances. a "field flattener" can correct this to some extent, but they are designed for use at infinity. Apochromatic retractors made for astronomy, having very simple optical systems by photographic standards (commonly a doublet or triplet design, either air-spaced or cemented) commonly have excellent to outstanding central IQ. I have seen excellent bird images taken with such optics, but they are expensive, very large, and not at all easy to use.

Interestingly, the ad features a series of images of varying FLs to compare with the that of the lens's 2000mm FL, and it shows a strikingly sharp image:



I'd have to be forgiven to not believe the accuracy of the images provided, as well as the hefty price tag, especially when in the ad it mentions this:
Now, our store has been authorized by ebay and PayPal to accept even more than 10,000USD lump-sum PayPal payment. Your purchase will be protected by eBay and PayPal both. Buy it now with confidence.

Confidence?

[MossyRocks]

It should be a sharp image as reflectors when focused properly will give good good results. If you look at the image it was shot to show the lens at its best. The image was shot at sunset or sunrise which means it would have been cooler with less wind. Also it was pointed up instead out across the horizon. These minimize the amount heat distortion from the ground and wind that would have blurred or distorted the image. Also by pointing it up the amount of humidity captured was minimized Finally it was shot fairly close to the structure which minimizes the amount atmosphere that can distort the image.

[TwoUptons]

There’s nothing saying that image came from that lens, is there?

That could have been shot with a Nikon superzoom or something, or even cropped.

It’s just showing field of view at low resolution, so there’s lots of ways to get there...

So I wouldn’t use that shot as an indicator of the quality of that lens...

-Eric