I don't think any sub should immediately trust someone just because she says that she is a Domme, because not every woman who calls herself a Domme is a Domme. Not everyone is up to par on safety techniques or on how to use the tools of our trade. I strongly feel that the sub should be just as knowledgeable or more so as the Domme he is serving. After all it is ultimately his health and safety at risk and he should know enough to stop any activity that is being performed in an unsafe manner. Remember that a few moments of pleasure should not have permanent consequences.
Lets take spanking.
But that's not true. Do you know there is a huge science to spanking. No, I didn't know that, I just thought it felt good. Spanking can be sensual yet sadistic. You have to know the different affects of each tool.