I would post a couple ideas for building a freelance portfolio without working for free. I used each of the ideas below in my business every time I wanted to add a new service and needed to prove myself.
Building a freelance portfolio without working for free. IDEA 1
Instead of offering to work for free to build your freelance portfolio, start out by building a site for your own business. Because you are your own client, this can be done around the hours you might spend on a day job. But, don't just make your site look pretty, go through the entire site design process, from ascertaining your needs, goals and objectives, to testing on multiple browser versions and even purchasing and setting up a domain name. This way, when a client says, "You're pretty new at this," you can say, "I understand your concern about the fact that I am new to freelancing, but let me show you what I have done for my own business, and explain the process I went through to create this site. This is the same process I would go through with you." Then, give them enough info to show that you do not just
"throw up a page," but that you go through a distinct planning phase that takes their needs into full account. This shows that you are a serious business owner who thinks about goals and objectives and how the web as a marketing tool can help achieve them. If you are lacking in actual experience, the best thing you can do is to build your prospect's confidence by showing them that you understand the bigger picture as well as the details of coding a web page. This works pretty good for me and i have won many freelance projects with this tactic.