While that is possible. A lot of the old miners that use to turn lots of profit have all given up on mining. There are still a couple of people who claim to be make some decent returns. It is however well known by many that are profitable that it is a small amount of profit if EVERYTHING goes right.
Those are also the kinds of people who might mine up $500 of an ore. Wait months or even all year for the price to spike and then sell that single ore off when and if it hits peak demand.
There are also some areas that are known for having a single ore that will be high markup. Some of those spots are in lootable PvP and they are camped 24/7. Other ores are rate limited how much can even be looted in an area over time with a lot of competition and many low markup ores scattered in those fields that take weeks to sell for 101% markup if at all.
Mining is quite a tricky subject. People hate giving up any info if they find a way to turn a profit doing it. As it could hurt their chances of what they know if others start flooding the market since there is often not enough demand to go around.