Below is a basic description of how SEO works. Ask your designer to explain to you what they're going to do for ORGANIC search results in search engines, such as Google and Yahoo. Get their description in writing, cross-check it against this description and see how close they come. If your Web Designer doesn't follow these general guidelines, find someone who does. There's more of course, such as how many keywords are optimal, proper alt tags for images, etc. but the following is just a guide for you to know if they know what they're doing.
SEO starts with choosing your target market, and the keywords your target would use in a search engine to find your products or services, a set of keywords for each page. After selecting those keywords, they must be built into the actual page name, which is the link, a.k.a URL, that shows up in the address bar, which matches closely to the Page Title (encoded on the back in the 'Title' tag), and also matches the properly tagged first header 'H1' on the page (The H1 is should be clearly visible at the top of the page contents as a heading to anyone looking at your page). And then further, the content of the page must contain, multiple times, the chosen keywords. They should be in sentences, detailed descriptions, and/or bullet points, and in various formats on your page. These keywords are then placed in a meta tag on the back side called “keywords.” If any of these items do not match one another, or are missing, then search engines will either lower the grade, or simply not index them.So hopefully this explains how a Web site is built from the beginning with search optimization in mind. SEO should not be an afterthought. Whomever you choose to work on your project, they should work closely with you to make sure to get the right content, keywords, tags, headers, etc. so when searchers enter those terms, your site will be found in the search results for your target market.