Humans love to brag by nature. Your clients will want to show off their product at every occasion. That's better than any SEO.
As a freelancer, you have minimal ressources to start off. Proper SEO can be super expensive. But, you aren't an agency. You don't require the SEO as much as them. You have the power of CLIENT VALUE. That is your secret weapon. Give your clients all the value they feel necessary to trust you. As reputation grows, so will your values grow naturally.
Treat your clients as you would want to be treated.
Most of you clients are not going to be highly tech savy. Utilise that. Offer them services that seem proffessional and hard for FREE. Most agencies charge clients to the cent. That is also a perfect weapon to use against them. Offer some of these and you are bound to receive positive feedback. :
Bite the bullet and give more than what you know you're supposed to. It takes minimal time for you to set up what your client would spend hours upon. Help them and they will definitly talk to their surroundings about you. Eventually you may decide to change your ways but there's nothing I love more than hearing a honest
Thank You Jabak.Y