thanks for the link; I was looking for something just like that and couldn't find it.

I didn't even think about conflicting transactions in the mempool, but they've got to be mostly fee bumps and not double-spend attempts. My guess is even the double-spend attempts are not malicious; they're just people whose transaction hasn't gone through yet so they try again.

Yah I don't know if there's black market for bribing miners, but man that's got to cost a lot of money and it still isn't going to work most of the time.