Never your bank. For ad platforms, the clean pattern: YOUR card sits in YOUR ad accounts paying platforms directly; the agency gets manager access to operate campaigns without touching payment methods. You see every dollar of spend at the source.
The arrangement to refuse: agency pays ad spend and rebills you. It hides the true spend-vs-fee split, adds their margin invisibly, and, worst, means the ad accounts and their history live under the agency's billing, which becomes hostage leverage at breakup time.
Same rule across every system: your accounts, your payment methods, their access-role. The ownership audit takes two minutes and tells you where this rule is currently broken.