I first came across the concept below of Enterprise Sales helping customers to buy in a tweet from Marc Andreessen but it really resonated with me. 

There are often many people involved in a buying decision and the sales person's job is not just to ace the pitch and demonstrate all of the amazing features of their offering but to ensure that all the people involved have all the information they need well in advance of having to make a decision. 

Salespeople often think that buyers just need to be persuaded of a product's benefits and they will find the budget but it is rarely that simple, particularly with truly innovative or disruptive products. These products will, by their nature require change which is really hard in large organisations. Change also relies on a consensus to succeed. 

Also, even with a consensus on a products benefits, buying can be properly difficult. New products often don't fit into existing budget silos and hence building a team approach is again essential. 

The good news is that the buyer is often really grateful to the salesperson for helping them achieve their goals, which strengthens the relationship and confirms the sales person as a trusted advisor to the buyer.