alt Hacker NewsI believe (I have done very little sales, so mostly as a buyer) that while all three (buyer-pull, seller-push, Cialdini-style mentioned in a comment below) can work, the best result comes from buyer-pull when you have empathy for the customer.
You try to understand the needs of the buyer, and see if what you are selling aligns with those needs. This is needed for effective buyer-pull, because they might not understand what they really need, or how what you are offering might fulfill those needs.
For a startup it is important to not be pulled to too many directions. If you find one great customer you can co-develop the product with them, whereas having very many customers might take up all your time listening to them.