I have had excellent experience purchasing Microsoft software from eBay vendors. I have advertised the great deals in Microsoft forums, we have discussed them. It seems that some companies buy software in bulk and are left with extra copies (License Codes) which they sell at deep discounts. The downloads are from Microsoft websites.
Since I need to support many 3D file formats (Import/Export), I cannot possibly pay for regular retail price. Autodesk has to be the greatest 3D company on earth.
I decided to pay $29 for this deal:
Well, it turns out that eBay and that vendor are selling exactly the same cracked version which is going around.
This is the Google Drive used to distribute that program: