Wire vs Certified Check

I’m buying a new car with cash and trading in my old one and the dealer says they need a certified check in order to do a same day transaction – I don’t have an in person bank and if I want to do a wire they say it could take multiple days to process it? How does this work as I don’t love the idea of paying days before I drop off my old car and pick up the new car, like could they claim my car has new mileage or anything else after the fact? Do I have any other options that I’m not considering for easy payment? Feels like a certified check should not be the default payment solution in 2026 with online banks being the norm