I 'd not guarantee that much for a new client before launching some test campaigns for 1-2 months. I'd do decent planning. There are two things to pay attention - one is price per client that client should have to be profitable and other thing is real price per client they will have after launching the campaigns. Profitable price per client will depend on margin that client has on that product (service). If it is 30% for example, then you should make a sale for max 20% - $1k. If clicks in search cost $1 to $10, then you can make about 100-1000 clicks. So your conversion rate should be 0, 10-1%. That is normal conversion rate. I mean It is achievable. Also you need to look into history in analytics how their website is converting traffic from paid or organic channel, or other channels. You can google conversion rate for your type of business and other metrics and then offer a good plan to the client without strict guarantee.