Do birds need to be seen by a vet?

I was looking online to buy a bird from someone local to me. Everything seemed right, the pricing and such. But I asked if the birds had been checked out by a vet and the seller just responded w “birds don’t need to be seen by a vet”. As a buyer I would think they’d at least check them as I heard they can have diseases that can be passed to humans and any vet visit could prove them to be healthy.