Unique models?

Yes. Just contact an artist here to do the project. Express to them your desire for the model to be exclusive rights to you, not to be resold in the store here. Then negotiate a fair price based on that stipulation. Once you guys agree on the price, go ahead and use CGT to "hire" that artist for a project at the price you agreed to. Just as you would for any project here on CGT. Go to that artist's profile, and click the Hire button.

When you're setting up the freelance project in cgtrader, there is explicit chckbox "allow designer to resell project result on the marketplace". If you will leave this checkbox unchecked, it will automatically means that you will own commercial rights to the model and designer won't be allowed to resell it. You are already covered by cgtrader, so you don't have anything to worry about.

@luxxeon, designer only sees it if contractor has checked this option. In that case when designer reviews the project, he sees something like "you are allowed to resell the end product on the marketplace". Unfortunately there no indication if this option is unchecked, which i consider big overlook from cgtrader side. I think designer should see "you agree to waive commercial rights to the model and therefore you are not allowed to resell it on the marketplace".

Current implementation of this option, may easily lead to misunderstanding and should be fixed by cgtrader.

Thanks for the info. I agree it should be more transparent. I am also not against the artist selling the model ever....just not before I get to release whatever I'm going to use the model for.
Maybe another option would be a "timed-exclusivity" option. Would leave some more room for negotiating prices in some cases.

I must agree with Lemonade here mate, if you contact the owner of the model then I can't see them saying no. I would always give this option to a buyer if they asked.