I would recommend your friend put down at least 30% (if possible) on a veh. which is outside of the “certified used” range and pay no more for it than the Kelly Blue Book Private Party Value to get the best rates. This is also possible with dealers of non-certified used vehicles because they are slow and hurting right now.
I’m bearish in interest rates for the next 3-5 years. I wouldn’t worry too much about a var. rate auto loan jumping into the stratosphere. Just study the index and payment caps before signing up and keep the payments under 60 months, preferably to 36 months.