As with every negotiation it's not about what the seller (you) want, but what the buyer is possibly willing and able to pay. Look at their ROI. If it is positiv

As with every negotiation it's not about what the seller (you) want, but what the buyer is possibly willing and able to pay. Look at their ROI. If it is positive, they will buy. Your goal is to take as much as possible of that ROI for yourself. So it's really about being well-informed about those numbers and then just explaining them, sticking to it and walking out, if necessary.