parry its not effected by expertise in pvp
NPCs have fixed avoidance amounts (outside of buffs). Players will change based on their gear.
Rogues, Monks, Hunters and Enhancement Shaman, however, can Parry in addition to being able to Dodge. The thing is, they also tend to have quite a bit of Dodge as well by virtue of the Agility they'll naturally be seeking out. Your Expertise will work towards that Dodge first, then Parry.
Assuming it is a 3% base for both Dodge and Parry (and I don't actually think it is, but that's moot for the moment) than all they would need to do is have 1% more Dodge from Agility or Dodge Rating (unlikely, but entirely possible) for them to re-introduce a 1% chance to Parry you. If they had 3% Dodge from their gear, they would have the full 3% chance to Parry you once more - though they still wouldn't be able to Dodge you. And odds are they're going to have quite a bit more than 3% Dodge from their gear.
Conversely, plate-wearers (save Holy Paladins) will tend to have much more than 3% Parry as a result of the Strength to Parry conversion. This means you may well have enough Expertise to knock off the base 3% of each (again, assuming that's accurate which I don't know that it is) but you'll still have to content with whatever their stats are supplying them with in the way of additional Parry.
Plate and Monk Tanks will have more of both as a result of spec and gear, while Druid tanks (like myself) will have more Dodge. This puts you even further from the goal just by virtue of their stats against yours.
Please report any Code of Conduct violations, including:
Threats of violence. We take these seriously and will alert the proper authorities.
Posts containing personal information about other players. This includes physical addresses, e-mail addresses, phone numbers, and inappropriate photos and/or videos.
Harassing or discriminatory language. This will not be tolerated.