As hard as it may be, practising the art of silence after an offer has been made, may just induce extra concessions. Reason: psychologically, the other party will react by thinking about the worst possibilities.
A minute of silence may seem like an eternity ... but it's only sixty seconds (perhaps a very profitable sixty seconds if you can extract "extras").
At the conclusion of this lengthy period of silence ... simply say, in a business like manner, "Would you please restate the offer, in its entirety".
You will be surprised at the extras voluntarily given, simply because you have not indicated your position.
Very often, negotiation points need to be repeated in order to grasp the full significance. These phrases are handy in order to elicit a repeat of what has been said.
"Could you expand on that?"
"Tell me more ... but first, please repeat the important points you've just made".
"What do you consider are the most important aspects of what you've just said?"