A fast exchange can leave price, authority and scope unresolved. A quiet week can contain a scheduled review. Count progress by the decisions made and information obtained, rather than by the number of messages.
Pacing means arranging when discussion, checking and decisions happen. Ask who needs to review what, and agree a realistic next contact where possible. A missed date then gives you a specific point to clarify.
Time already spent does not make the remaining deal worthwhile. Compare future costs and benefits when deciding whether to continue, pause or decline.