Much of this is steeped in buyer psychology. The best marketers in the world know that there is a psychological process that must occur for prospects to whip out those credit cards and turn into buyers or even hyper-active buyers. One such person whose perfected this process is Russell Brunson, an "underground entrepreneur" who founded a company called ClickFunnels, a sales funnel SaaS business that empowers marketers from around the world to build marketing automation without all the hassle.
Unfortunately, most people instinctively distrust marketing material. Generally speaking, most marketers tell the story that puts their offer in the best possible light. After all, marketers make money off of telling people their product is great. Maybe your offer is as good as you say it is, but it’s hard to believe someone who gets paid to talk about how awesome their offer is.
Prospecting and marketing are all the things you do to get people into the first of your sales funnel stages. Note that stages are broken into two or more steps wherever possible. A demo could be called a single stage, but in real life it involves a lot of things: contacting the customer, sending reminders, doing the demo, and then following up. Whatever your own sales stages look like, the support you need in managing them will be the same.