mediumwhat am-i

The cost of making only the maker knows, Valueless if bought, but sometimes traded. A poor man may give one as easily as a king. When one is broken pain and deceit are assured.
Common Wrong Answers
“Gold”
Gold has intrinsic value and can be bought or sold, which contradicts the idea that it is 'valueless if bought'.
“Gift”
A gift can be valuable and is often given with the expectation of appreciation, which does not align with the riddle's emphasis on valuelessness and deceit.
“Secret”
While a secret can be traded or shared, it does not involve the notion of being 'broken' in the same way a promise does, nor does it imply the same consequences of pain and deceit.