Using tables for layout is not standards compliant and could adversely impact page loading times. (not good) The more code in your page the larger the file and the larger the file the longer it takes to download.
Updating and maintaining web pages will be much harder, and could take longer, which may translates more being more expensive.
When you think of your website project try thinking ahead and plan for the long term. You want a site that is extendible and can be managed more easily. Best practices are not called such for no reason. I stress this point because it's an important one.A portfolio will give you a glimpse of what the designer / developer is capable of will allow you to see the design style. Any web designer with sense won't include customers in their portfolio who were not happy. It's bad for business. Searching for a good designer in reputable online listings is a good place to find a web designer or any other service for that matter where the company or individual will be rated by the public.It is of greater importance to that firm that they perform well since their rating is available for the public to see. An example of such listings would be Yahoo's Local Search listings, or online Yellow pages. A good source for finding a good web designer is to speak to people who you know who have had first hand experience and who built their web sites. If people have been given good service they usually don't have any problem recommending their designer to you.It is OK to ask for a mock up site. Usually designers will tend to make 2 mock ups for you to compare and sometimes they may even show you an array of various web styles and templates prior to commencing. This is a way of narrowing down the style, how many columns, colors and themes he will need to design for.The web developer needs to advise you on every aspect of the design process. He should educate you and explain in very plain terms the reasons for doing things. Don't just take his word for it. Ask why. He needs to give attention to what content you intend putting on your site also, because SEO is all about content, keywords and relevance. Obviously the content decided on is ultimately the client's decision, but a responsible designer should inform you of how you could optimize your content. It is important to note that some web designers usually are not experts at SEO and there are specific SEO companies or individuals that do just that, however it is best if they work hand in hand with the designer of your website. If you do find a web designer that can do a good job of SEO then you stand a better chance of your web site being easier to market and rank.So here are a few points I believe would make an overall good choice in a web designer/developer.
Expresses the importance in planning your site for user friendliness
Understands good web design that is standards compliant
Can think through the eyes of the potential visitor of the clients site
Uses colors well and researches the target audience.
Educates the client and explains web terminology in layman's terms.
Plans a site from SEO perspective, with attention to file structure and naming schemes.
If doing any programming, all the above applies and also strong focus on usability of the application. Easy user interface, secure and full featured to name a few..
These points are by no means the hard and fast rule, its just a guide. However, I believe most importantly above all, you should get good service. Good quality service is the best marketing tool for any business and you should expect it.