Initiating negotiation with customer proposed price

Imported from previous forum

We’re trying to model a case where customers initiate negotiations with a dealer at a proposed price. This is different from the usual RFQ workflow which starts with the customer requesting a price from a dealer via a QuoteRequest message.

Would it be appropriate to start such a negotiation by using QuoteResponse [QuoteRespType=Counter]? The issue I’m facing with that is that I need to communicate two times: the time the proposed price is good for and the overall negotiation time. I can use ValidUntilTime for the former, but since QuoteResponse doesn’t have an ExpireTime like QuoteRequest (I understand why that is), I can’t communicate the latter.

Any thoughts/pointers appreciated.