Author is in a far better position than most projects, since he 1) already has companies using his software and 2) has folks from those companies contacting him

Author is in a far better position than most projects, since he 1) already has companies using his software and 2) has folks from those companies contacting him directly for help. Corporations are in the business of making money which also puts them in the business of spending money. They pay for office space, things to put in the office, people, services, insurance, and software. They pay for everything. There are hardly any things they don't pay for! So as long as the math makes sense and the transaction is presented properly, they are happy to shake hands and pay for your services. In fact, they want to pay you to make problems go away. Red Hat is worth billions for executing this at the corporate scale. Free software is just the hook. Corporations that can pay for software now have money to spend on other services. This realization is what made Red Hat. The only thing you need to know when freelancing is that if they walk away, they were never shopping to begin with. They were just gaming you. Everyone knows labor isn't free. So if they really need your help they'll pay. And they'll expect market rates, so charge them market rates.