Well, I think that having a website is better because it's international, and more people go on the web because it's a lot easier to view, and people like seeing things through the internet better.
it does depend a lot on your business too - but a web presence of some sort will enable your customers to feel connected to you and trust you better etc etc (twitter/fb/google+ style)
It definitively makes at least a small improvement, in my opinion. I think there are many people who like to check things out using the internet, also people who go to google and search for a similar business are more likely to come across your website.
Therefore the website is more likely to increase sales.
Also as Senff said, the better the website the more likely it will increase the sales.
Does having a website really increase your sales?
Do your customers judge you on the quality of your own website, or is a portfolio of work (without website) merely enough?
Without a website would you get just as many sales?
James.
A good website will increase sales.
I think there are many people who like to check things out using the internet, also people who go to google and search for a similar business are more likely to come across your website.
Therefore the website is more likely to increase sales.
Also as Senff said, the better the website the more likely it will increase the sales.