The third option is hardly ever the correct play and is niche. That leaves the 1st option and the 2nd option. The 1st option is really only if your retail stores sell televisions for a WHOPPING 10k+ and you're running out of TVs fast, while the 2nd option is the better case, based on 1.2-1.4x(optimal buying price based on several factors). You don't wanna sell when it's only a marginal profit when you can instead sell every now and then for a larger profit, right?
Alas, these are only baselines. The price changes all the time because of some indirect buffs when adding things into the game (you need more of a rss now) or an indirect nerf (the factory is now outclassed by a better one)