Selling to Carvana. When do you get your money?

My friend called me for advice. He has a 2012 Toyota Tacoma in great shape and 100k. Carmax offered $16,400 and Carvana offered $19,000. The Subaru dealer he bought his next car from offered $14K

If he agrees to Carvana and has his clear title in hand, do they trade him for it with a check? How do we know the check will clear? Any other advice?