I earn substantially more on freelance over my typical 9-5. It really comes down to confidence in my own ability and presence, feel(ebb and flow) with your client. I charge by the job, which is where the confidence comes in...it may take me 9 iterations to get it right or maybe just 2, and sometimes I get it on the first try. I enjoy this method as I work through til the client is thrilled and I push myself in the meantime.
People seem to really get into the handshake deal, most of my clients are referred to me. They feel they are a part of the process, that they have a say. The relationship is what matters, if you make your client feel that they are being heard and taken care of then they respect the value that you place on your services.
Something I find to be very important, is being honest about your workflow and time available. Inflate your sense of timing, and then come in slightly under that mark.
Granted I have the security of a well-paying 9-5, so I can gamble a bit on my freelance...but that gamble has more than paid off.
I am upfront and honest about my limits in hours, walking the tight rope of just enough billing info to give to the client.
Typically for a kitchen remodel and small additions I tell them it will cost between $800-1.2K for takeoffs/as-builts, $4-5.5K for arch CD's and design(which credits the as-built fee), and another $800-2.5K for structural if I can perform prescriptive work.
Leave room to charge for additional services in case you are getting tanked by the agreement.
I put place-markers for cabinets, and let the cab vendor do the finite details and add a couple renderings. If you would like me to design the cabinets and prep an order I will charge. If you would like additional renderings I have to charge for the potential income from my rendering machine being down..etc, etc
Going over projected cost is all timing though, and hopefully you never need to.
I explain that the design process is the fun part, and is inexpensive in retrospect to all of the annotation work and county req's. I manage my CA time log to get a feel for my target revenue.
Hope this helped, a different perspective maybe