Bitcoin transactions work via smart contract, meaning that both parties have to "sign off", or agree, before the transaction can be completed. Bitcoin is very similar to cash in this way. Cash transactions can only occur if you physically place cash into someone else's hands, whereas bitcoin transactions can only occur if you send the Bitcoin to complete a checkout. Therefore, it is impossible to claim a fraudulent bitcoin payment for the same reason you can't claim a fraudulent cash payment: you have to actively complete the transaction for it to be valid.
It is very important to set up the correct security protocols to protect your bitcoin. You can do this by:
Setting up a strong password with a password generator.
Enabling 2FA for your account, so that even if someone does manage to guess your password, they would still need your phone or personal authenticator to verify a transaction. For more information on 2FA check out the "My Account" section of our help center.
Never let anyone know your private keys, under any circumstance.