In GF1, when Michael met with Sollozo and McCluskey for their last meal, the Corleones insisted that Michael have a "negotiator" from the Bocchicchio family to act as a "hostage" so if Michael was killed during the meeting, the Corleones would kill the Bocchicchio hostage and the Bocchicchios would take their revenge on Sollozo for breaking the deal on a peaceful meeting.

However, why didn't Sollozo get his own hostage/negotiator to protect himself in case he was hit? That seems like a terrible oversight. I understand that they knew Michael as a "civilian", but still, Sollozo was careless not to plan for this. After all, he did frisk Michael personally, even after McCluskey frisked him, so Sollozo was obviously worried. I'm also surprised that Sollozo didn't have some of his own men hanging around at the bar, just in case.

This seems terribly naive of Sollozo, and he paid for it with his life.

The book goes into more detail on the Bocchicchio family and how they served as meeting hostages; in the movie, there is a passing reference by Clemenza about a "negotiator" playing cards, but if you hadn't read the book you wouldn't understand the reference.