Happy holiday

When the buyer says, let me talk to my boss, and I will get back to you. This means that the deal just lost momentum, because you are not part of the decision anymore.
In psychology, we call this decision diffusion, which means that once the conversation is move on to someone else, it's not conveyed in the way you would have said.
For example, the buyer/ the staff might go back to their boss, and he might explain your offer, but he would simplify it. So, it wouldn't be the same as how you offered it, and main points which would have been very beneficial.
Instead, you can ask this. May I ask what would your boss would be more focused on when he's reviewing this offer? Or you could say something like this. May I provide you with a short summary which you can deliver it to your boss?
This way, he can take your message as it is the way you presented, and the boss can see your offer In your way, because if you're not part of the decision, you are not shaping the outcome.