"To finalize the deal" means to complete or conclude the agreement or arrangement that has been negotiated or discussed. It implies reaching a final decision or taking the necessary steps to make the deal official or binding. Full definition
The helpful sales team will provide all of the information and details that you need, and you could surely finalize a deal as soon as possible. (depaula.com)
However, they'll only finalize the deal if they can sign a replacement. (sbnation.com)
He eve... n stayed late to finalize the deal because he knows when I'm serious I am going to purchase. (cars.com)