I've seen some action on a coin I was monitoring on BSC using poocoin (similar to dextools but for bsc - it shows buys and sells). Whenever there was a big buy/big sell on this coin, there would be an (arbitrage? frontrun?) bot that positions their transaction exactly one position after this large trade (for example, a normal person sold a large amount at index 43 of the block, this bot would have it's index at 44 of the same block, always one position after the large sell, and makes a profit from this).
What I would like to know is how does this bot (using minimal gas) manage to always position their transaction exactly one index after a big sell? I know it's not a case of higher gas, because the bot uses normal gas fees. I've also seen bots like this on ethereum, where their transaction is always directly before/after a large trade on uniswap (for example).