you mean they spend to one address and then immediately spend to their own address? using a higher fee to incentivize that the second transaction gets mined instead of the first? My understanding is that that won't work on Monero because the second transaction will also contain the key images from the outputs in the first transaction and consensus won't allow key images to appear twice. so there will be a race condition between the two transactions. memools that have seen the key images from one transaction won't relay the other one. and the first one has a head start so it seems unlikely that the second one would propagate across the network.