This is a good question. On the one hand, the "honest is the best policy" mantra of our childhoods comes to mind. But the truth of it is that if you are completely honest, you are going to get taken advantage of, and other people are definitely lying, so it puts you at a disadvantage.
So in an absolutist moral sense, yes, it is wrong. On the scale of awful things you can do, though, it's pretty low.
I've been on both sides of it. I've lied about my current salary during negotiations (I was being dramatically underpaid, and didn't want that to be used against me). I've also had a customer tell me they got a lower quote for job. When I told them to go ahead and accept the other one, since I knew mine was competitive and if anything, a little under priced, they came back a couple days later and accepted mine.
Personally, I wasn't offended by the lie. I know they were just trying to get the best price possible, which I had already given them. It was my responsibility not to let myself get low-balled.
Perhaps a better question is whether you are prepared to deal with the consequences if the truth comes to light. However slim that chance may be, I feel that's a pretty good rule of thumb for grey-area moral decisions.