Is this a used car scam? I don't know how to respond.

I heard my cousin bought a car, so I checked the history after seeing it,
and it shows a 4-year rental history.
He said he wasn't notified about this and was told it was a single-owner vehicle driven by a woman.
When I called to confront them,
at first they claimed they had disclosed it, then they said they didn't disclose it because it was a lease and driven by an individual,
and finally, they called my cousin and said
that the only difference between a lease and a rental is the payment method, and since leases also use "Ha/Heo/Ho" license plates, it's the same as an individual owner.
I have all the recordings.
Also, the performance inspection report shows no minor leaks,
but since I have an acquaintance at Bluehands, I had it checked, and they said there is a leak near the chain cover that requires repair.
They said they would take the car in and fix that.
It seems like once it's fixed, a refund won't be possible,
and they are lying, gaslighting, and even threatening not to fix that part if I get too angry.
My cousin wants a refund even if it means taking a loss,
but is this a valid reason for a refund??
I've heard some say that
failure to disclose a rental history isn't enough for a refund..
The contract for the car was signed on September 3rd.