A quick look at "template" websites.
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Templates:
A design someone else has
Limited customisation
Some use of Flash which will not work on iPhones nor allow for good SEO ranking.
Lack of mobile optimisation
Lack of support if something goes wrong.
Use of outdated technology
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"Custom" sites in comparison to "template" websites:
Better SEO
Adaptable to business needs
Scalability - Upgrade your website to an ecommerce site.
Ability to easily maintain the website through a Content Management System (CMS)
Copyright material (pictures) obtained
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Source:
Web Page Mistakes
Our own thoughts
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At Radian Web, we create websites, we do not use templates. Check out our website page for more info.