How many troops does he hold? And what is their quality?

In case they are good and fairly numerous, I would say we could bargain for them.
For instance we could demand the troops to be release as a sign of good faith, and then the exchange of money and the Count. That should leave Robert to have no real option for deception. We get the troop ahead of the exchange and get the money as we hand over the Count.

If the envoy refuses, so what. It isn't as if we need the money that much, nor the troops. However I find it important that we are perceived to be a good lord who will help his lessers in cases such as this.
But I won't trade back for rabble. So my proposal only stands if the troops are good and somewhat numerous.

Did we lay the proposal on the table?