How do you write restock replies without promising too much?

A shop operations question about restock dates, supplier uncertainty, and customer choices.

Customers usually want a date when an item sells out, but small shops may only have partial information from suppliers, makers, or delivery schedules. “Soon” creates repeated messages, while silence loses buyers. I think a restock reply should separate confirmed shipment, estimate, next check date, and substitute option. How do you write restock replies that are useful without sounding like a guarantee?