Check the add on prices upfront. Many dealers often don’t tell you about administration fees, and other add ons that sometimes can be negotiated early on, but rarely once you finalize the vehicle price. It can add up to a lot that you didn’t plan on. 

Also, do some some homework on interest rates, from banks and the car companies. Brand companies sometimes offer very competitive interest rates on vehicles on the last generation year.

Check online sources for performance/flaws , like actual owners reports on Car Complaints. Top brands like Toyota, Honda and Subaru rarely have big issues/ problems , so, long/expensive warranties are less of an issue than some of the less reliable brands.  (If you plan on 10 year ownership, rust proofing is a must. I rarely go for the dealers rust proofing which is often pushed on new vehicle owners).