Also, for any FOSS author who gets one or more of these inquiries don't laugh it off or write blog posts mocking the sender. Take it as the business opportunity it is and send a professional response indicating your willingness to help them navigate through this, at least as it relates to your bit of code, for customers with paid support plans. You want money, they have money and you can trivially provide them something at least some of them are willing to pay up for with a potential opportunity for a non-trivial longer term relationship.

This is the best kind of sales call: they are coming to you.