We've recently moved into a house we had no idea had a dog smell. I love dogs but not in a position to have one right now, probably because of this, I didnt see the previous owners 2 dogs as any kind of issue. I do now!! 
When we viewed the property it was sunny. Windows were open, coffee brewing etc. Not a whiff of dog.
The day we completed we entered the house and the smell just hit us like a sledgehammer around the head.
Its vile.
The house has wooden floors downstairs and carpets upstairs. After shampooing upstairs carpet 6 times in 2 weeks (twice with neat dettol and the rest of the time with different brands of pet carpet shampoo), using numerous bottles of neutrodol carpet deodrant and shake n vac, febreeze etc etc the smell wouldnt shift. We replaced the carpets.
We still have doggy smell (been in almost 3 months) in the hallway. It has wooden floors that we have steam cleaned, polished etc. We have even had the radiator off the wall (there was a whole dog in hair behind it) and washed and scrubbed every inch, yet all we can smell is bloody dog!!
We've washed walls and even repainted too. Still can smell dog.
We are having a few radiators changed in other rooms but have decided to change the hall way one in a last bid attempt before the only thing left - to lift and removed the solid oak hall flooring - one of the things I loved about the house!!
Sorry to waffle on but my advice is - assume the worst when thinking how easy/difficult it may be to shift the smell.