Problem with a recent purchase

I bought a used Toyota Corolla S 2013 about a
month ago for college. The total price was $10,220
so I paid him $8,000 and the rest I have to pay
within 90 days in two separate payments. When I
first got it, the check engine light was on and the
guy from the dealer told me I could pick up the car
the next day so that their mechanic would fix
whatever the problem was. So it turns out they
didn’t fix it they only  disconnected the light (I found
out myself). When I first had a passenger in the car
with me, the “air bag on” light turned on. And the
guy who sold me the car never told me that there
was a problem with the airbag system. I still have
not paid him the rest of the money. Any
suggestions on what I should do? Btw when he
showed me the CARFAX report I didn’t see the part
where it shows the information about the airbag or
else I wouldn’t have bought the car. When he
printed the CARFAX report I noticed that the scale
of the font was huge AF! So I’m guessing the guy
printed the report zoomed in so that the airbag
problem wouldn’t show on the printed version.