Do you want to negotiate with a private seller (Craigslist) or use fixed, pre-negotiated pricing (CarMax)?
If searching for a specialized or classic car, specialized auction sites like Bring-a-Trailer often have better quality control. good websites to buy used cars
Do you prefer in-person dealer inspections (Cars.com, AutoTrader) or online, no-contact delivery (Carvana)? Do you want to negotiate with a private