A suggested revision to your licensing blurb (proposed revision in italics):
"If your application restricts any of these freedoms, such as commercial or closed-source applications, then the GPL license is unsuitable and you must contact us to buy a commercial license at [email protected]."
"If your application restricts any of these freedoms, such as commercial or closed-source applications, then the GPL license is unsuitable and you must contact us to buy a commercial license at [email protected]."