security of paying someone using apple pay

You cannot get your money back; you can only cancel it if the other person hasn't accepted it yet. Also see the following from Send and receive money with Apple Cash - Apple Support

In your Apple Cash transaction history, person-to-person payments appear with a name, phone number, or email address. If the transaction status says pending, the receiver hasn't accepted your payment yet, and you can cancel it.

Apple Cash person-to-person payments are like any other private transaction between two people, so only send and receive money with people you know. 

Apple recommends to only send Apple Cash to people you know. No refunds are possible once accepted, which is why the person you know would be a trustworthy person who would send the money back to you if asked. It is a person to person transaction where you are taking the responsibility for the cash that is sent.

The most common use case is to send money to family and friends and commercial use is strictly prohibited in the Terms of Service.

It is against the Apple Cash terms and conditions to use a direct person to person payment for commercial (business) purposes.

https://applecash.greendot.com/termsconditions/

This is one of the major reasons that people experience their Apple Cash (Apple Pay) accounts.