The skill Master Poisoner is supposed to give you a total of 3% Crit on your target if you have any poison on it.
Master Poisoner Rank 3
Increases the critical hit chance of all attacks made against any target you have poisoned by 3% and reduces the duration of all Poison effects applied to you by 50%.
However currently, its giving you 3% Crit on each stack of Deadly Poison. Since Deadly Poison can stack 5 times. Its giving you a total of (5 stacks x 3%) = 15% Crit!
Pretty pimp for all rogues since it ups your Crit % by 15% instead of 5 and its OP for killing raid bosses. Talk to your raid leader that you can bring + 15% Crit to boss fights to get one of those raid spots that everyone is fighting for. Passing it on to rogues to that don't know before this gets fixed, but I don't take credit for the exploit.
Here's some links for proof, notice Cleavis Crit% jump from 6% to 19%. Bring a friend and try it out for yourself and bang on a test dummy for a hour or two and notice the differences in in your friend's Crit%.
WWS from autoattacking a lvl 80 dummy with a 1h sword and maxed sword skill
Wow Web Stats
~6% crit rate
WWS from autoattacking with the same gear on a lvl 80 dummy with a constant 5 stacks of deadly poison
Wow Web Stats
~19% crit rate
by G00DFe77a