I think in a situation like this, I would ask the client what the goal of his site was - does he want bells and whistles to show off, or does he want customers buying his products to stay in business? Because in this particular case, it seems like it would be one or the other.
If his goal is to show off,
SEO really doesn't matter because visitors will hate the site anyway (if you can, check the bounce rate of the site, might be a good way to prove your point) and search engines will spam flag it.