One of the other forum posters stated it best, "Deception is HARD mode".
This is a viable PVP class, but you're going to need to work at it. Having a razor Naga or something comparable is almost mandatory.
You can't rinse and repeat command rolls with deception. You need to pick you targets. You can't get into a one on two plus if you want to stay alive. You need to learn how to run. You need to learn how to use SLOW, Low Slash, Control Abilities and be smart with them.
You can't play on auto pilot. Will you beat an expert player tank one on one? NO. Will you be able to take a true expert DPS build? NO. Will you be able to ax a healer? YES.
For better or worse you are dependent on players being distracted. You need to be opportunistic. The whole point of your build is positioning, planning, striking and getting the hell out when things go wrong.
I can't tell you how many times I was able to use most if not all of my talents to bail out a group mate in PVP and Flashpoints.
Last, don't forget your taunts, you can mess things up, create confusion, and get out before you get killed.
It just takes skill, dedication, and watching what works with other players.
Youtube helps for those who need to be shown.