I think that while yes, you have to be safe in kink and you have to know what you're doing, the bottom line with all risky play is trust between you and your partner. There are many things that I do with my sub that I would not dream of doing to someone I had just met, purely because they do not know me and they ultimately don't know what I'm capable of.
In reference to the original post, therefore, one of the best play sessions I've had with my sub was to pretty much use things that were on my body at the time as restraints: my neck tie held her hands together at the top of the bed, my belt buckled around her feet, my shirt stuffed partly into her mouth and her flat-backed hairbrush was used to administer a good spanking. She informed me of how much that stung, especially when I dragged the spiky side across the painful areas of her bottom.