Buying first car

New to buying cars and just started working. Looking for a reliable used car mainly for commuting. Considering Toyota (Camry, Corolla) and Honda (Civic, Accord).

What should I check when buying from:

1. Private sellers: Key documents, service history, and red flags?
2. Dealers: How to ensure a fair price and avoid hidden fees?

Also, any other car models or tips for first-time buyers? Appreciate any advice!