I would really like to drop some minor references to all the 12 guilds in DDrop, in order to set up any future games we might work on. The dream of my 13-year-old gamer heart is to make a Delver's game in each RPG sub-genre, including turn-based (JRPG style), tactics / strategy, true roguelike, etc.
Anyway, as for shops having different prices, that is something I would probably work into the characters' perk trees - so the Rogue could upgrade perks to get lower prices, and so on (or better selling prices). As for shopkeepers being fightable / killable, stealing items, etc, I'm honestly not sure yet. I was actually trying to prevent shopkeepers from being (or even looking) attackable, mainly for technical reasons - it would be hard to animate one more character using the humanoid skeleton that the playable characters use. More art for 8-directional movement, more animations / more-detailed animations for attacking, walking, etc. But I will try to come up with something interesting or secret that can be done with shops.
As for all the other guilds, I actually have a list of the other classes loosely thrown together, totallng 3 classes per guild. These are not set in stone, and might change from game to game based on the needs of the gameplay systems or balance. So like final fantasy, in one game the Hanged guild might have a Rogue, Assassin, and Executioner, and in the next the Executioner might be replaced with a "Noose-Cutter" or something. As long as it still fits the theme of the guild, I'm okay with assuming that in the DDrop world, that while the guilds are set (there are always 12, and they have a consistent theme), they are somewhat organic in their members, and classes can come and go or change to something slightly different. So as another example, the Assassin might become a Headhunter in another game - they are still one who targets someone for capture or assassination (and therefore fits into the Hanged guild), but they might slightly have different mechanics or backstory.
I sent Vasae the list of all the guild/class ideas if he has time to post it up here, I'm cool with that being public. Just fair warning that the classes won't necessarily be referenced in DDrop, and it's all subject to change!