Which Database use in Desktop Application in .Net.

Question

I Will Create the Billing Software for Client but problem is that to face the Databse problem which Databse preffer. i have already made software with Sql server 2014 So When I Will delevered software to Client Computer then Sql server also Install on her Computer and Also when i make more than software than is is impossible to install sql server on client Computer.

So Please help me How to Resolve that Problem..