Found a Toyota rav4 hybrid. Do l place a deposit before the PPI? Sign paperwork before ppi or wait?

Found a 2019 Toyota Rav4 Hybrid. It has 65,000 miles and they want about $27k for it. It's hard to find anything close to my price range here because they sell so fast. I'm debating whether I should put a deposit down or sign anything before completing the pre purchase inspection. How does that work? Thanks!