The structural difference
With an ISO, you are the acquirer’s customer; the ISO is a sales channel. With a payfac, you are the payfac’s customer; the acquirer sits behind it as infrastructure. That changes who answers the phone, who decides your underwriting, and how fast anything happens.
Neither model is inherently better. A good ISO can place hard cases with the right acquirer; a good payfac gives you one accountable counterparty and days-not-weeks onboarding. The failure modes differ too: an ISO can’t fix anything after the introduction, while a payfac inherits its sponsor’s constraints.
Questions that reveal which you’re dealing with
Ask: who is my contract with? Who underwrites me? Who do I call when settlements pause? If the answers are “the acquirer, the acquirer, and the acquirer”. You’re dealing with an ISO, whatever the branding says. If it’s one name for all three, you have a direct counterparty.
Then verify the counterparty the usual way: regulatory registrations you can check, structure explained without prompting, pricing categories named up front.