That’s a great question- I agree with your answer and thoughts on it. A big part of selling any item is the feel and confidence that you get when purchasing it but also the factual performance of the product or service itself. Were you provided with enough information to determine that the product in question will make your life easier or is it necessary in some way? Will it fulfill a need or issue that needs to be addressed? If the salesperson cannot answer these questions from a technical standpoint, the purpose of purchasing would not be clear to them and the sale would be lost. On the interpersonal skill side, if someone tries to sell you something and they do not believe in the product or service themselves, it would most likely be reflected in their body language and enthusiasm. If they do no have confidence in the product, it is hard to push that confidence onto someone else. I would say that both are essential parts, as well as several other skills such as emotional intelligence and professionalism. It can be hard for a salesperson to accept “no” for an answer and walk away on a professional note in the case that the buyer in question changes their mind or would like a different product of yours later. It is for this reason that emotional intelligence and professionalism are essential in sales as well.