I know this is a topic that has been beaten to death recently, but I've had some first-hand experience I think relates to this and I want to get some second and third opinions.
When I was querying agents for my first novel I had a 60+% rate of return on agents asking for sample chapters or the whole manuscript. But for this new book, which is a better book with a better query letter, I am 0-30. I had some luck early on with two agents who I've dealt with previously, and one agent who contacted me on a referal, but for blind submissions, nothing but form letters.
I talked to a friend in the business, and she and I both think it's because I identify it as a PI novel with a traditional PI plot. My first reaction was to rewrite my query letter referring to him instead as a security specialist doing skip traces, and call it a "thriller for the media generation" instead of a PI novel for the media generation.
Then I got an even better idea. I'd make him a detective with the Detroit Police warrant squad and have the PI he was moonlighting for be a skip on a murder warrant. The changes wouldn't be that major and it would actually make a lot of things easier.
But here's the problem. First, I REALLY want to write a PI novel. I love them and love the tradition and want to make my own contribution to the genre. And I know it's not a totally dead genre because Sean Chercover is getting some good press for his debut, and Dave White recently sold his first PI novel for a decent deal.
The other thing is that the agent who contacted me through the referral was very excited about my book, though he had some problems with the plot and motivations which he asked me to rewrite in a detailed letter. Would changing the character be too much for this rewrite or would it show I'm aware of the market and willing to adapt? My initial instinct is to keep it as a PI novel for this rewrite and then if this agent passes, do the job change and requery with that then.