You will see a resurgence of power leveling services, item trade services, and gold farming. Classic will have a fresh economy meaning for your average gold farmer time spent in classic is way more efficient. It will probably be worse than it was back in the day. Just look at the blizzard group finder on retail, littered with advertisements for m+ boosting websites. Disgusting. There will be so many gold farmers blizz probably won't be able to keep up. And this is what I truly fear because if the gold farmers start to win activision will step in and introduce wow token. And classic will die.
An advice for those who are trying to compete monopolizers: you cannot beat them by selling for less if they follow right steps. You should do opposite: sell for more. Because market will come down if the price goes unreasonably high. You can set a bid on item for the price it should cost and buy out price for higher than a monopolizer is selling. So, common buyer may get an item for the right price or monopolizer has to buy the item at his loss.
For the duration of the fight, creatures in the immediate area will not be visible to you (but they may still attack you if they wander too close). Keep in mind that other players will still be able to see you and attack you if you are eligible for player vs. player (PVP). Other players will also be able to view your pet battle in real time, including the pets involved as well as their health as the match progresses.
To get Blacksmithing to level 300 is much effort. It is not that thing to make fast gold. There is always a lack of Blacksmiths though. Enchanters need rods of all kinds, melee classes look for Sharpening Stones and Weightstones with Counterweights, others buy Iron Spurs. Once you have learnt rare and epic recipes, people will always use your service to craft items.