The wizard who built and staffed the dungeon you’re looting helpfully left weapons, medicine, scrolls, books of mind-bending arcane power, and magical replicators (aka “save points”) laying all over the place. Security be damned, there are rules of hospitality to observe.
You can sell 5000 swords to a shopkeeper who lives in a town with a population of less than 50 people. Not only won’t he run out of money, the price of swords will remain completely unaffected despite you flooding the market.
Spells with awe-inspiring name like “Annihilator of Worlds” and that you have to work toward for most of the game will turn out to be useless due to having no effect on major enemies, horrible side effects, or high costs. No, the truly useful ones are usually low level ones that scale up with the player level, like “Slow”. Unless “Slow” can be resisted in which case it only affects kobolds.
The people that you meet in a game are remarkably broad-minded, and will provide goods and services to a blood-drenched necromancer every bit as cheerfully as they will to a shining paragon of goodness. Dwarves, however, will occasionally be a bit snotty toward elves.
Nothing that you must have to progress in a game ever requires picking a lock to obtain unless you’re playing a lock-picking simulation.