is there a sensible way to sell seo?

sell a small fixed thing first, not a retainer. look at the prospect's site for twenty minutes, find three specific problems with a clear effect (their main service page isn't indexed, their title tags are all the brand name, their business profile has the wrong category), and show them. that's the pitch, it proves you looked. offer a fixed three-month starter with a short list of what you'll do, never promise a ranking. and be picky, pick clients whose business can turn traffic into money, because a client who can't is one you'll lose in six months no matter how good the seo was.