I have webgl build platform that sell products using ethereum and metamask.
button code in c# is like:

 public void Send50()
{
    Price = 50;
    StartCoroutine(SendTransaction());
}

obviously user can change price with developer tools. If you say move transactions on the server site how it should be done? that means after that user will not see the metamask pops up and send transaction? is there any tutorial?