Internet is one of the most rapidly developing spheres and there's no wonder that it requires more sophisticated approach. Today Internet marketplace becomes more specialized and so IT professionals target their work in smaller areas.
Take a look even several years back and you will notice at that time only few professions have been available on Internet. At that time a programmer could do almost everything including SEO. Nowadays specialists in narrow fields are needed, so you can find such professions as information architects, web designers, Google Adwords managers, SEO analytics and various types of program and web developers.
Unfortunately, in many cases web designers have no idea what SEO is and do not take into consideration its principles while creating website design. Just take a look at code of some websites and I bet you will find ones without heading tags or metadata. Even though it's extremely easy to add, designers don't because they are simply not aware of crucial importance of these small factors.
Here is where buyer suffers the most. Money for design is paid, whole website looks very stylish and eye-catching, but not many visitors will be able to value it because they simply won't find it. This situation is particularly true for heavy Flash websites. They often look great, no one's going to argue, but Flash implies graphics and images cannot be read by search engine bots. This means Google and others will render them like images, even in case there are words. Sure, no SEO success is possible for such website.
When you are about to hire a web designer, you should check profiles of potential candidates carefully. Even though some mention search engine optimization somewhere in their marketing material, many know nothing or very little at this subject. Check website designs in the portfolio of candidate, then visit his/her own website. Look if there's any metadata, do pages have description, keywords and page title is in h1 tag. Look, what pages are on that website - something useful or just welcome message.
You will need just a couple of minutes to check these. When the page is open, make a right click and select 'view page source' (for Google Chrome) or 'View' - "Page Source" in Firefox. You will see website code. Metadata is usually near page top. Then check page title and scroll website code. If you see any h2 tags in the text, this means your designer is really ware of SEO and knows how to apply it.