If you use PayPal on your website pages, there's a really easy way to find out for sure. You can ask your customers as part of the checkout process how they found out about you - and I've noticed that most customers do actually answer the question even though it isn't compulsory.
I've also noticed from doing this that a high percentage of my customers come to me from a search engine. A healthy percentage are word-of-mouth recommendations. Only a few found me originally at craft fairs, so that route was less effective than I thought it might be in bringing website customers to my virtual doorstep.
If you want to set up your PayPal so that it asks customers a question about how they found you, open your PayPal account and go to:
Profile > My selling preferences > Customise your Payment Page.
Then click on the options tab and check the add a customer survey button. Write your own question and your own multiple choice answers!
It's not perfect, but if you're running a small online business, it gives you a really good idea of where your customers are coming from and that, in turn, might make you rethink how you promote your website.
For me, my blog is key in getting those search engine visitors into my shop! What about you?