As many know, MMO and multiplayer are plagued by bots farming or harvesting resources/items/etc.
The following principles will deter bots from a game forever(at a cost of course)

1.No progression RPG: all attributes/weapons/equip/skills/stats/perks are selected at character creation screen and do not change withing game.
Game doesn't feature economy or items, weapons are class-locked. Other character builds can be examined via website form or in-game so no secret special builds exist.
Solves: Everything, but progression is absent.

2.No-item gameplay, no inventory/trade possible: all item attributes are converted into skills/passives/perks , combines with skill-use-to-level system for progression.
More realistic option, but completely eliminates economic influence(nothing can be sold in-principle if nothing exists) and makes the game explicitly skill-centric.
Solves: Everything except character trading and rushing services(can be discouraged with low skill level cap).

3.Zero-economy games: Trade between players is forbidden, items dropped on ground cannot be picked by anyone except item owner(drop owner). First one to pick a drop(monster/chest) owns it forever,(items can be still sold to vendors).
Essentially every item is account-bound on pickup.
Solves: Everything except character trading/account training/rushing.

4.Account-binding magic items: all items that have some value are account-bound on pickup. Least restrictive. Combine with vendors selling resources/consumables cheaply to discourage resource farming.
Solves: most of item farming. Currency/Consumable farming can be discouraged with limits on maximum trade cost.

5.Trade-cost cap: Limits trade to items below specific maximum price.
Solves: casual item farming.