It does what it says on the tin.
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I've done hundreds of this type, but usually only pirates because you will almost certainly become wanted and that may be tedious if it happens after your first kill..over 70k per ship is ok (plus possible bounties), but I use the benchmark of 50k for pirate kill missions, so 20k more isn't much for the added difficulties of killing clean targets, especially when you factor-in guaranteed bounties on pirates.
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I only accept illegal kill missions in designated systems around my home system for convenience - it is easy to operate when wanted, I go about my business normally, but you need fast docking skills and to be aware of situations that can get difficult.
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If the system is an anarchy - forget all of the above...but that is unlikely, so if it has a CNB or HazRES this will help; normal RES will be off limits coz of your inevitable wanted status and USS etc may become problematic when the cops turn up.