Great points all!
When I still worked with clients, in cases like this I often used a takeaway close that worked 50% of the time.
I'd explain, like everyone in above said, why no one can guarantee rankings. But then I'd say something like this...
"I understand that getting a guarantee helps you feel more confident about their service. So if you totally trust that this company can deliver what they promise, then for the price they are offering, I say go for it! What do you have to lose, but some time and some money?
Since I don't feel it's ethical to offer a guarantee since no one can guarantee what Google will do, and since I won't paint blue sky, or just tell people what they want to hear to get their business, I realize my service is not a good fit for everyone. I think you should go with them - give them a try.
Some of my best clients came to me after trying another service that could not deliver on their promises. So realize I'm always here for you, if and when you need help down the road. I wish you the best of luck though and really hope this works out for you!"
Now when I speak it, it sounds more natural than what I wrote above... But there were some important psychological triggers I used in the statements above.
"So if you totally trust that this company can deliver what they promise" Brings up the fear.
Of course they don't trust it.
"I think you should go with them - give them a try." - At this point I'm saying this honestly, it's not manipulation. I really do think they should go with them and don't want them as a client.
BUT they don't want to take a risk and give someone a try. They want someone they can trust to deliver results! What they EXPECT me to do is start giving them the hard sell or some other kind of sales pitch. If I do that, I lose and they walk.
What I did was the exact opposite of what they expect. I totally backed off and gave them permission to walk away, if they really think the other solution is better.
That builds trust!
So the reply I would get 50% of the time when I tell them to go with the other company was: "Wait, Wait! I didn't say I was going to go with them, I just wanted a guarantee. But I understand what you are saying and even though your fees are higher, I feel more comfortable working with you."
If they end up instead going with the other company, then you've left the door open for them to come back to you down the road.
Haha, YAY Dragon typed most of that! I could not have typed all that. I needed to do tons of corrections, but we are making progress!