I would ditch the client!
Seriously, if you’re not into Flash or you’re not happy doing what he wants advise him to find a developer who doesn’t care if the project is successful or not and is happy to do anything for the money. You’re the professional and you’re telling him his approach is wrong or inadvisable - if he’s not wanting to listen then he is either stupid or does not value your input, in which case why are you working for him? You’ll only end up developing a site you’ll never be happy with, and he’ll come back bitching that it’s getting low search engine throughput and you’re the one that ends up looking like you can’t develop a search engine friendly site. Whats worse is he’ll tell his mates and colleagues that the site you developed for him is a flop which will only further harm your business.
Personally I only do sites which I’m happy doing - if I feel uncomfortable I tell the client (nicely of course

) to look elsewhere for a developer.
"I’m too busy and not taking on any new jobs at present" seems to work well.... I spent too many years trying to be everything to every client and it got me nowhere, Now I’m more choosy and the result is my business is a damn site better and I’m enjoying it again.
Thats my two cents. I’ll be interested to know if others agree of if I’m just an SOB!