While the the best of them offer surprising amounts of flexibility, they also impose stringent enough restrictions to page design that you shouldn't be able to create a really bad looking site using one of these services. Typically you can get a Mysite.servicename.com style-url with no commerce abilities for free from one of these services; you have to pay extra for a better URL and the ability to sell. One issue to consider is that if you eventually outgrow one of these services, it can be hard to export your site to a full scale advanced web hosting like Dreamhost or Hostgator. If you know that's where you are eventually going, it may be better to skip the sitebuilder step.
You need to understand your audience like you do your very own yourself. You are aware of your dislikes and likes, you know what problems you face and you know the sort of people you will let help with those problems. If you learn to know your audience in the same manner, the chances of you establishing a genuine connection increase vastly. You will also be able to guide more people through your sales funnel and get those coveted ‘closed-wons’.