Assume, for the sake of argument, that I am a miner and that I am ready to cheat. The (stratum) pool server sends me a
notify message and I start mining. I find a valid share. I
submit it to the pool server (which, presumably, checks if it is valid). Now, what happens if I re-submit it a little while later, in order to artificially increase my number of accepted shares?
So stratum pool server keep a list of submitted shares and check for de-dups? On large pools, where miners report a share every few seconds, this means keeping about 16kbyte of data for each miner, and scanning through it every time it submits a share. So it seems feasible.
But is it actually done?