For me it was arrows. Could buy the stuff to make arrows and sell them to the merchant for more than it cost. First macro I ever put together as well to do it quick. That was during macroquest before the 2.
Yup, and really it was bow cams! I recall mq1 and early mq2 days trying to optimize movement routes and such for making cams, was only 10s of thousands an hour if i recall but it was a big deal back in velious/luclin days
Early days of EQ and most all of the expansions all had huge bugs. Either to dupe, tradeskill for $$, wrong loot tables, low hp or dps mobs, pathing issues etc...
Earliest bug i remember was pathing bugs like the cave entrance to runnyeye you could AE mobs that would never be able to climb up to you (which is main reason we have summoning mobs!)
Similar pathing bugs as well for necros was fun times, move a few feet and the npc would run a loop or long route to get back to you, so you could med for a few seconds and dot up a mob and let it run around.
One of the dupe bugs during velious/luclin era.... while camping your toon was still in the world for <1second after logout and database save, so you would get a toon to super low HP and use druid nuke (faster the ice comet so easier to do timing) and if you time it right you get back to char select with all your gear, then log back in and loot your corpse and repeat
Various insta/fast spawn mobs or mobs with low hp for their level so you could powerlevel either solo or group content for first few weeks of expansion till they were fixed.
Various new expansions bad loot table stuff, or items that get removed from game....so the first week or two you could get gear, so it was critical to take time off work to farm the first week or two of expansions instead of rushing to max level.
My favorite long time running bug that was never fixed (maybe it is now) on red servers you could proc weapon procs (like avatar weapons!), or skillup melee/spell skills by attacking corpses