bots use a limited amount of tokens set on the player's potential. You'll pay somewhere around 30-40 ko rounds worth for a 5* very fast trainer.

Also, from the bids i followed, they do join ONLY on random gen players and not on normal real players' ones. I do think then that those are either automated or the ones using them have filters for only gen players. Yesterday i warfared 30 rounds for a player and the other guy had Q27 bidding over a q 45 gen. Each time the counter hit 3 secs left the bid arrived.