In psychology, how are delusions clified as either "bizarre" or "non-bizarre"?

In the DSM-IV, schizophrenia can be diagnosed if someone has no other symptoms besides delusions, but they must be bizarre and persistent. Delusional disorder has no other symptom than "non-bizarre" delusions. But I've read some examples of these non-bizarre delusions and they seem bizarre to me. Likewise I've not seen any source in all my searches that has a good, objective answer to how the distinction is made.