Should I be nervous about Yield Spread Premium

I have a GFE from a broker that contains a hefty (>$8000) Origination Charge that includes a 2% Yield Spread Premium, and a credit for the whole of that amount. The rate is good and the broker insists there are no points to pay, but I suspect that what will happen is that once underwriting starts the YSP will suddenly drop and I'll effectively be paying points at closing anyway. The broker claims that any differences in the YSP when underwriting starts will be covered by them, but when I asked if they would put that in writing he said that they could not.

Is this normal practice? Should I be nervous?