> Personally if my bank was also in the business of spying on financial transactions commercially... I wouldn't feel super secure about my choice of bank.

Are you aware that your (bank-issued) credit card purchase data is almost certainly sold commercially, linked to a unique identifier?

There's companies that buy mobile advertising data and crosslink it to credit card purchase data to track real-world conversions from online advertising.

I say this to reinforce your suspicions, not to discredit them.