I usually don't like salespersons because most are pushy. I just want to be left alone and when I need something I'll ask them. When I do need their help, I expect to be treated like a human being. Not some number. A salesperson should know a lot about the product that they're selling. They should be able to answer almost all my questions. Of course they can't know everything and that's alright.
Good service when buying a product is important. But the service after you bought something is even more crucial. Problem with delivery? Broken? Not what you hoped for? Anything could happen. Customers like cheap prices but they love good service. If you treat them right, they will reward you back. It will not always end up with the customer buying the product but good feedback is very worthy too. If they say I gave them good advice and that I was very friendly then they just made my day!
So to summarize, A salesperson needs to be friendly and ethical when dealing with a customer. If you do that, you'll be gold!