Some notes on zero profit for retailers:
I owned a video game store during the PS1-N64 era (1995 - 1999) and I can tell you that back then, there was in fact zero profit on new consoles. It sucks on the surface, but there actually is alot to be gained for the retailer by selling them. When I sold a customer a console, chances were extremely good that they would keep coming back to my store for games. Another benefit that it was rare for me to just outright sell a new console, in most cases the customer would want to trade in either an older system (or systems in some cases) and/or games for other systems. Used items are by far the most profitable items for a retailer because it's your only chance to buy low and sell high. But in the long run, you will profit from the sale of a new console, even though the actual sale of it gives you nothing at the time of sale.
As for keeping them in stock, you just have to be smart. For a small independent store like mine, I had to be very careful in my ordering. I would normally keep 2 to 4 PS1's in stock and replenish them as I sold them. You actually have to be even more careful in ordering games. On some occasions (not all), when the price drops on a console, the manufacturer will actually reimburse you the difference on remaining units in your inventory. Sometimes. Sony did this for us on the first 2 rounds of price cuts on the PS1, but not after that. But they NEVER do this for games. So if I ordered 4 copies of a game and sold none of them, when I drop the price on them it cuts directly into my profits. And eventually they will be sold at a loss. That part really sucks, but it's the same concept as the consoles: If I don't have the new games, I won't get any used games in trade. So I would generally only order games that I knew would sell based on customer's talking about it and if they were sequels how well the previous titles sold. Some were just instant money, like when the new Madden would come out I'd get as many as I could get my hands on and sell them the day they arrived.