When I ran a search firm the number one conversation around the watercooler was fees; clients trying to reduce them.  They'd site competition, the economy, whatever.  My response was always the same; NO, unless there was exclusivity, volume or some other circumstance that compensated the reduction. The principle is simple: the belief that the value received from my service is far greater than the fee itself.

It goes something like this: After having a 20 minute conversation with a potential client we get to fees.  I start with we are at 25%, 30 day guarantee and it's non-negotiable. This, of course after I sold the value of our process and have their affirmation. They would usually respond by telling me xyz recruiting firm works at 15% with a 90 day guarantee.  My inquisitive response would be; if you were satisfied with their service I'd imagine we wouldn't be talking. Amazingly, the sales pitch then shifts from me to the potential client as to why we should accept their business. This is a rarely used approach but works most of the time. 

I know to some this may sound extreme but trust me. It's based on this principle. There is a phenomenon called the Stockholm Syndrome.  In psychology, Stockholm Syndrome is an apparently paradoxical psychological phenomenon in which hostages express empathy and have positive feelings towards their captors, sometimes to the point of defending them. These feelings are generally considered irrational in light of the danger or risk endured by the victims, who essentially mistake a lack of abuse from their captors for an act of kindness.

Now, we're not talking a hostage situation.  In recruiting terms, the more firm you are with potential clients, without hurting them of course (in this case demonstrating value) the more likely they are to align with you. People generally want to be liked and will acquiesce and want to please; even when paying. The added value is an agreement to [your] terms exponentially increases the probabilities of an attentive and motivated client. They'll believe that you have some secret or something better to offer then the other firms. The trick is; you better!