Hiring a mechanic to rebuild your engine, paint your car, and post it to Ebay motors is only bound to have implications. The web design and marketing business is tight nit. We don't compete as much as you think. My firm provides fully disclosed outsourcing services to many of the other firms in my area, and vice versa. That's how we are all able to offer such a large pallet. Regardless, if I don't excel at something I won't submit it as part of my service offering. You need to determine what these firms are capable of before hiring them.

Marketing agencies are good because they understand how the website will fit into your current marketing strategy. You want a team that can handle both tasks though, either with in-house staff or through strategic alliances. However, some marketing agencies don’t have good designers and programmers on staff. The average graphic design student entering a job out of college can definitely whip together print media, but not necessarily web layouts. The reason programmers are not user-interface designers is because the right (creative) side of their brain just isn’t used as much. It is very odd that you find a balanced individual, and those rare specimens are usually flash developers. They understand how to create visually stunning works of art, but also understand actionscript.

Remember, marketing outweighs technology every day. You could have the coolest back-end technology ever. Your content-management system could be purely AJAX driven and off the charts complex, with integrated color wheels, batch photo sharing capabilities, newsletter generators, etc. You could have your entire POS system integrated and be making other developers drool. How does that help sell your product though? The presentation layer of the design is what the end user sees and is what will persuade them to become a customer. You do need to find a good programmer however if you want certain things to work well. SEO is easy when the architecture is designed right. You users will definitely enjoy a site that’s cross-browser compatible and complies with W3C standards. Programming and design are two different disciplines. One can argue all day about how they are an expert at X, Y, Z, but at the end of the day it’s just a sales pitch until you see results. I would not hire a programmer to design my U.I. You should look at using different sources that can augment one another to meet your needs.

So in essence what you need to find is either a firm that has staff members that excel in all these areas, or find multiple consultants that can work together as a team. I would hire someone to create the U.I. design first, and then worry about the programming. During the development stage, specify to the programmer that the site needs to be setup to maximize SEO. After that find a consultant, that specializes in SEO, to go out and get you those high search rankings. If the programmer says he cannot work with the U.I. design, then find another programmer