No offense intended but when you sell it like that "We are staying a bit high to put our resources to the most efficient use" it basically screams like bullshit.

It'd be much sweeter sounding to just say you're developers, recruiting other developers, so you can vett them much better than career recruiters can. Offering that level of vetting is more time consuming, thus you are offering a premium service.

However, you might be better off sticking with the bullshit sounding answers, becaues I imagine your market isn't us, it's the business who can't vett their own guys.