Cannot review product

I had the same question. Here is the answer I got from the support team.
How to rate models you purchased: You can update the rating on the "My Purchases" page. You need to simply press on the "Rated" button next to the model you wish to rate.
I'm a seller haven't purchased anything yet here. If you still have the issue, I suppose support team will kindly help you for sure.
Hope it helps!

Hi there,

Thanks for reaching out.

There is currently no possibility to review a free model, but you could leave a comment if you like to.

Kindly,
Greta from CGTrader

I purchased two models, one has broken textures unwrap, the other said it included .unitypackage but after import it was just the .fbx. I want to rate these models so others can avoid feeling like they were scammed, but how? When I received the invoice for my purchase I click on REVIEW button but nothing happens.

Sites that don't take the reviews process seriously are destined to fail, I refuse to support shady / lazy sites I can't trust. Please fix your review process so it is fair.