I've known of a service that actually provides APIs. I cannot remember what it is called but such services exist for hotels and holidays too.
Iirc I stumbled upon one of the flight tracking services by pure chance.
Having said that, I feel like Skyscanner at the very least has their own systems in place. There have been times where I've chosen a ticket, have gone through to the website that sells the ticket at the price, and just before it goes through, Skyscanner validates that the price still exists, and then bails saying the price has increased or decreased. Usually it's not by a lot, but it has happened.
Iirc I stumbled upon one of the flight tracking services by pure chance.
Having said that, I feel like Skyscanner at the very least has their own systems in place. There have been times where I've chosen a ticket, have gone through to the website that sells the ticket at the price, and just before it goes through, Skyscanner validates that the price still exists, and then bails saying the price has increased or decreased. Usually it's not by a lot, but it has happened.