My regular masseur has one posted rate and never has "specials." But oftentimes, he will discount a session for me, as a long-time client, without my asking. Sometimes the discount is substantial.
I would always come prepared to pay the masseur's posted rate. But I don't check his ad all the time, so I might not know if he changes it. If I did know of a change, out of respect to him I would bring it up and offer to pay it. I think he would say to just continue paying the former rate but I feel I would owe it to him to be upfront.