Have you ever called your mortgage company to complain with how they charge you? The Electric company? ... No of course not. So my rule is.. I don't explain it. This is my fee, take it or leave it, business owner's do not need to explain or justify their fees if a client complains. Once you do begin to do that, you'll find yourself always having to explain why you are raising rates.. This is a crappy economy, this is the way the world goes around. Explain it once in your contract, if you are billing a flat fee you do NOT need to go into detail how the fee is calculated, beyond explaining what the fee includes. If you signed a lease, your rental agreement price is listed in the lease but it's not explained how they got to that fee (insurance, taxes, etc etc) I had one or two clients question me about increases and when I moved from percentage to flat fee, but I really didn't comment, if they asked why, I simply explain what I just said here.