It doesn't matter how commercial or unique your work is, let's face it, you're unknown and unpublished (Kindle doesn't count) so most people won't even look at your query, let alone go to all that trouble of reading the pasted sample. Hence, in most cases, the rejection will be based on your query letter or, worse, on genre/word count/the agent not being open to submissions at all. That's one of the reasons why you shouldn't take rejection letters personally, but here's a few more:
1. Agents don't usually mean to belittle writers because they're professional. Hence, even if an agent tells you they wouldn't know how to sell your work, it doesn't mean your work's that bad but rather that they don't have the necessary contacts (i.e., editors) to whom to talk about your work.
2. Every published author has been rejected at some point. Even the big names like JK Rowling, Anne Rice, Stephen King. Yes, all of them, and if you don't believe me, then by all means go on and do a Google search. So, you see, rejection isn't necessarily a reflection of how bad your work is. It's simply a matter of taste, time, risk, being unknown, living in the wrong part of the world etc.
3. 'This isn't right for us' means exactly that. You may have submitted the right genre, but the agent may not connect with the work. Remember, taste is relative, particularly when it comes to humour and style. So, be grateful for the answer since it's become common practice not to give any answer at all, and move on to the next bunch. You wouldn't want to be represented by someone who isn't fully committed to your work anyway because your project deserves the best attention it can receive.
4. Perhaps you weren't convincing enough in your query letter? If the rejection letters keep flooding in, don't hesitate to take another look at your query letter. The culprit might be right there.
Even if no one shows any interest in your book, don't give up because there's more to publishing than finding an agent or publisher. Work on building an audience platform for your next book and keep writing. Sooner or later, you will get noticed.
To your publishing success!