Well, just for the sake of fairness, whilst I tink this salesman was doing completely the wrong thing, I think I should mention I have bought shoes from Runners Need 3 times now, and they have always been great with me, very happy to take time with me, explain everything and watch me on a treadmill and talk through what they suggest. They've also been happy to suggest shoes which would not be 'in their best interest' if they were soley commissioon searching - they basically tried to downsell me (when my heart was set on Asics) to a NB pair which were nearly half the price, and in fairness felt pretty good.
I think Cougar's right, they offer advice, it should be taken on board, but the decision & responsibility is with the customer.
Oh, and finally, I would phone and ask to speak with the manager, and explain your recent experience. I'm pretty sure that when he hears your story, and hears you are not a newbie and you are a club member with lots of running buddies with ears, he will be more than keen to listen and speak to the salesmen (not assisitant!) about his approach.