1) One way to do it would be you and seller go to your bank and get a cashiers check for the amount. This will give the seller confidence that your cashier's check is real. If out of state you may need to get a bank account with a major national bank.
2) Then you both go to the DMV and do the title transfer and the seller takes the cashiers check. if it's out of your state then maybe skip the DMV and do whatever your state requires to transfer the title (signed title, bill of sale, any notarized requirements, etc).
3) Take possession of the car.
There is always some trust required so if something seems off then it probably is.