If you authenticate with <mortgage broker> via Plaid, then the broker pays plaid money and the broker gets your bank information. So I suppose in a sense that's "selling your data," but I don't think that's what people are concerned about: You explicitly sign into the mortgage broker to give them data!
What Plaid has said on record they DON'T do is take that data they provided to the broker, bundle it up, and then sell it to marketing firms or hedge funds or other random third parties for which the user didn't explicitly ask their data to be shared.
“Plaid does not sell and has never sold consumers’ personal information or data. Consumer data is obtained and used with consumer consent. Plaid believes strongly that consumers should have permission-based access to and control over their financial data, and embodies these principles in its practices."
