They are a business and have to make money, but if they treat customers fair then they will keep them, if not - vote with your feet and avoid the rip off merchants.
An RFD has to be at least 20% more than a private sale or they don't make money, but second hand stuff up for near new price is a way of convincing you that you may as well get a new one, so don't believe they always want to sell that second hand one they have, it can sometimes just be a marketing ploy