Charging a fee based on sales would be reasonable. That's what Unreal Engine does (5% of gross revenue after the first $1 million). Charging a flat fee per ins

Charging a fee based on sales would be reasonable. That's what Unreal Engine does (5% of gross revenue after the first $1 million). Charging a flat fee per installation, even for games that have already been developed and released (many of them for free), is insane.