"Islam teaches that lying to the infidel is perfectly acceptable. So -- if a Muslim tells you that they condemn jihad, and if you are not a Muslim, how will you ever know whether or not it is the truth or a lie?"
I've been lied to by Christians, too. I've been lied to by Jews, Buddhists, and others. I judge whether someone is lying by their other actions, not just by their speech.
Since I don't know you, I have no way to judge. One of the Muslims I know lived two doors down from my home. I know him quite well, and I know him to be a truthful man. You...I don't know.
Then your Muslim friends should condemn jihad publicly, and they should have no problems.