@FIRA You are wrong.
1. By the Terms & Conditions you had signed when you joined CGT, you are personally responsible for the models you upload:
"18.1. Members may only upload Content they own or otherwise have the right to use and upload. CGTrader does not own any Content uploaded by Members.
18.2. By uploading a Product, the Seller shall be deemed to represent that such Product and use of this Product permitted by General Terms does not infringe the intellectual property of any other party and that the Seller had obtained all necessary model or property releases for use and licensing of the Product. All Members should consult their own legal advisors to determine whether a particular model or property release form and (or) any applicable contract is suitable or necessary for uploading particular Product or for a particular use of a Product, or whether such use is a fair use. Sellers should understand that licenses of Product without a release attached may be negatively impacted, if a release is deemed necessary by Buyers or their legal advisors."
So it's not your friend problem - it's your problem and responsibility.
2. Even if you personally buy Hum3D models, you are not allowed to modify and resell it. Check the license:
https://hum3d.com/terms-and-conditions/
"The CUSTOMER may NOT: redistribute PRODUCT or modifications/parts of the PRODUCT"