My 2 cents: I do a bit of freelancing on the side, with a yearly income in the lower 5 digits. I have a (very) basic website and a limited, but free data service, and I have created 2-3 opensource tools that are relatively well-known in the field. My impression is that I get most of my clients either via word-of-mouth, because they need some extension to a tool I wrote, because they want to get rid of the limits of my free data service, or because they found one of my papers by chance and need something similar. If they want a quick call, be prepared to quickly answer who you are, what you have done in the past, what you offer, how much it costs, and how long you have been doing this (large customers in particular don't like to take the risk that your business will disappear in 6 months). Write these answers down or memorize them in advance if you are not the social type. I charge flat rates for certain services, and around 110 EUR / hour for anything else. Be punctual for meetings, professional with you invoices, and answer emails quickly and to the point. Don't gossip about previous clients.