Unless you can fix how payment and financing works, it is extremely hard to sell or buy a car online.

This is why carwoo - as it is today - is doomed. Even after you have a deal, you still need to negotiate financing terms and that's when sales tactics come in. The same car can have many prices depending on which bank you choose, apr, etc.

People who pays cash for used cars are the minority.

Explaining why the same car can have many prices: Dealers also make money from banks. They get paid a small percentage of the loan presumed profit, the larger the profit (longer loans) the better. Dealers use that margin to negotiate.