Don't ask me. I was lucky in that I knew I did not want an agent. I was doubly lucky to find a publisher on the second attempt. I was triply lucky to find a second publisher. I was even luckier to find three editors who have given me the sort of encouragement and advice that a good agent will often provide. I was also very experienced at contract negotiations and other business issues, so was unconcerned at having to handle such issues myself. I suspect that a great agent is invaluable, but I have a suspicion that there are plenty of less-than-great agents around. Is it worth having a less-than-great agent? If you are writing non-fiction, I doubt it.