A live demo and a good visual representation of the features you have to offer is a great way to get buy-in. The personalized approach that is used also plays a big role in the buy-in process and your knowledge on the topic will make it or break it.
From experience I think that timing is the single most important factor, because I may not need something now, but who knows if in the near future this need would arise. There are also business constraints that will affect your willingness to spend money on services (ex. at the end of fiscal years, companies are usually more likely to spend their remaining budgets on your proposed services or products, not because your service is needed but because the budget needs to be spent).