Most secure form of payment for a large amount of money.

Greets!!

I've recently been in the market to sell a large box of memory. I've never done business with the guy before, and am driving out of state to do so.

I'm concerned about doing a transaction this valuable. It's $20,000 + and I NEED to make sure I get paid. What is the most secure form of making sure this happens?

Direct deposit, money order .... etc

I have a smart phone and am meeting the guy in person, so I can track any account from any location etc etc...

Any input would be helpful.

Thanks