I remember implementing very complex cryptographic scheme in pure C. After a week of hard work, my friend concluded: "Cryptography would be much easier if people just trust each other."

The truth is that it is my reputation on the line, so I also have to make sure dependencies I use don't mess up things as well. There is no good defense against it. In my contracts I undertake to act in a good faith and take the responibilites to the amount of my professional insurance. Honestly, it is different casy by case.