Well, this is a firearms board. Why would you want to advertise a cross bow on a gun board? We don't take sword adverts, nunchakku adverts or throwing star adverts either. I guess I could go on with more examples, but I guess the answer is if you wanted to advertise any of these for trade for a firearm, it would be accepted. As long as a firearms is involved we pretty much allow it.
Just make sure you read the posting rules and eligibility guidelines before doing it.
"The irony of the Information Age is that it has given new respectability to uninformed opinion." - John Lawton, speaking to the American Association of Broadcast Journalists in 1995