I think it is important for writers to understand why agents pick the projects we want to work with and why we pass on others. Despite what some writers seem to believe, we don't only select the projects that will make us a ton of cash with our select and exclusive group of editors we work with. But, with that said, yes, sales does factor into the project.
Obviously, agnets only make money when we sell books. That is just the simple, cold-hard truth. So, with that in mind, yes, we do look at whether or not we believe we can market that book in a fashion that we believe the author would want and one that will yield the best return for the author (and yes, for us too). But, our ability to sell that book comes down to several other factors that I do believe many author fail to remember.
First of all, we have to like the book. This is simple. If the book is something we don't enjoy, we simply won't have the enthusiasm to want to market it. I call this the brocolli principle. Think of the item(s) that we leave on our plate. In many cases (although not at my house) we leave the brocolli or some other food we just don't like. The same goes for the stories we as agents market. If we are totally in love with a project, we market it like crazy. It is the first thing that comes up in a conversation with editors or book buyers. We simply can't say enough. If we aren't completely crazy about it, we tend to forget it. It is simply off the radar. This is no reflection on the author or the book, it simply comes down to our connection to it.
Secondly, we have to love and understand the genre. Look, despite what some think, we as agents do not know every genre inside and out. Each genre has its own unique quirks and characteristics. Science fiction is much more than simply talking about distant planets and unique weapon and spaceship names. There is a unique voice. For that reason, we are likely going to pass on projects that fall into genres that we just are not connected enough with to provide the best editorial guidance. I'll be very honest, this is the reason I don't represent the fantasy and the sci-fi. I don't mind reading it, but it is just not in my realm of complete understanding. Hey, this is no different than mechanics. Sure, most engines work relatively the same way, but the differences are significant enough that mechanics specialize. The same goes for doctors, dentists, educators and so forth.
Next, there is the issue of who we currently have in our agency at the time of a new submission. If we already have a group of writers in that particular genre, we will not likely add a new writer in that genre for the simple reason that we don't want our writers to be in competition with each other. We would never want an editor to have to make a choice between two authors we represent. We don't mind it if they are writers at different agencies, but internally, this just isn't going to work.
Finally, there is the issue of connections. Yes, agents do meet a lot of different editors out there, but we don't know everyone. No, this is not an issue of being in New York, it simply comes down to the time we spend together at conferences. If we don't have the connections, we might not be able to fairly represent your book. In many ways, we are throwing darts just like many writers do when they mass query every agent or editor out there. Without the connection, the sales just doesn't go through. For me, this is one reason why I don't represent the general inspriational category. The connection necessary to dive into the CBA market are pretty extensive. There are agents out there that have those connections and for them, this is perfect.
Hopefully you can see that when we look at projects, there is a bit more than simply the quality of the book.
Scott