Don't feed the business practice you don't like.
Offer to buy with a down payment, with some expected delivery date, balance to be paid at completion, just prior to shipping.
I'm pleased that Dream-Hammock.com has adopted what will become, I hope, a "when-will-the-bus-I'm-waiting-for"? chart at his web-page. Sets a standard for custom work, and could be yet more informative with another column of expected delivery date. Proprietor doesn't have to stop sewing (or hiring) in order to answer calls and emails about status. The home page tells customers to expect a six week delay.
In another Forum where anxiety about unstated and variable delivery times are also a concern, an HF member points out that he knows the variability across vendors. JacksRBetter.com maintains inventory of most of its products and ships within a day unless the item is out-of-stock. No drama, no suspense.