When we receive a gift, we feel a need to reciprocate.
Give things away for free. A free account, a free report, a free workshop, a gift card etc. Preferably something that people won't expect to get for free. People will feel the need to do something in return, whether it's buying something at your shop directly or referring friends (which you can make easy with social media integration).
Note: if your competitors are also giving things away for free then people might also expect this from you and it's no longer a real gift.