If you're contacted by a member whose profile states that they're a couple and they reveal that their wife is unaware of hubby's presence here please report the private message so that we can take care of it. Likewise if you're contacted by a member whose account states that they're female and they reveal that they're actually a male it should be reported as well. Private messages themselves should be reported, not the user. This enables the staff to view the private message in question.
As previously mentioned, there is a "Bisexual Cuckold Club" section and all postings of a homosexual nature should be posted there and only there. If someone posts homosexual type stuff anywhere other than in the appropriate section it should be reported as well.
Regarding unsolicited private messages, yeah. It's annoying. As long as we have an open forum it'll never completely stop. It's not only limited to gay men looking for BBC. Most everyone here gets unwanted PMs from time to time, increasingly so as a user increases his or her social footprint on BtoW.
The easiest solution is to ignore the user and they will no longer be able to contact you. If the private message is rude, offensive, or violates any of the forum rules it should also be reported. You can also adjust the privacy settings in your profile to limit who may contact you.