There already is a delay, that delay is ping. You can't list multiple items at once due to ping. I like to be able to list my items fast so I don't want a delay to be added. If there is actually an issue with someone using a bot to list then thats up to the devs to ban them for using 3rd party software on the game.
I always list bulk quantity usually but it takes me 7s to make 10 listings, I don't want it to change to be 27+s for 10 listings.

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