Squidy, how would the salesman even know if you needed a longer zoom or not. I am always a bit skeptical when talking to salesman. Maybe it is because I have to deal with salesman at work all the time. You have to be able to make your own judgment call because most will mislead. (whether on purpose or because of their own ignorance). As far as the 75-300mm it is better than having no lens at all. It is a starting point and the range will get better from there.

You had a post not long ago asking about the 70-200mm for portraits. Maybe a better question to ask the forum is what would be the best lens for your intended purpose and the price range you can afford. There might be a cheap prime that would work for you, or a combination you haven't thought about.