What if i purchase a car through CarGuru and 3 days later it turns out to be a lemon, as a buyer do i have any protection, or guarantees?
CarGurus is just a listing site. You purchased from a dealer or a private seller and you should talk to him. There are laws protecting this behavior by a registered dealer, but less protection from a private party. Check laws in your state and consult a lemon law attorney. In California, an attorney will provide an initial consultation free.
If you are worried about this only buy a car that has a buy back guarantee in writing.
I would pull a history report and look here: https://cargurus.helpscoutdocs.com/