New York’s financial regulator is putting crypto marketers on notice: a waived commission is not the same as a cheap trade, and any claim otherwise now has to be backed by records an examiner can inspect.

The New York State Department of Financial Services issued an industry letter on Nov. 12 that treats advertisements built around the absence of a single charge as potentially deceptive when they leave out the costs customers actually bear. The guidance, signed by Acting Superintendent Kaitlin Asrow, applies to every virtual-currency business the department licenses or charters in the state, from BitLicense holders to limited-purpose trust companies.

The department cited “no-fee trading” as an example of a claim that can create a false…