My wife used to be a recruiter, and had what you are asking happen to her several times. She would spend hours screening resumes, doing phone interviews, presenting the candidate to employers, and generally making things happen. She was always very careful to align the candidate and potential employer, making sure they were a good fit (not always easy to do). So then, the employer would get excited about a particular candidate and make an offer, which my wife would relay to the candidate. Too many times, she heard, "Oh, no thanks. I was just practicing my interviewing skills." Hours were spent (and lost) on somebody who was, more or less, abusing the good will of the recruiter and employer.
I guess it's like going to a car dealership every weekend and spending two hours test-driving cars. When the salesman tries to work out a deal, you just say, "No thanks, I just like new car smell," and leave. That salesman is on commission, and you just wasted a quarter of his day when he could be dealing with a serious buyer.
Not to get into the question of whether it's fair to your employer, you are wasting the valuable time of both the recruiter (if there is one; there usually is) and the potential employer. Not only is that not nice, but you have burned two more bridges. The recruiters all have databases of candidates, and they keep notes.
On the other hand, if you want a recruiter to really work for you, I have found the following phrase to work magic, "I am serious about my job search, and if I find the right job, I'll accept it." Just like everybody else, recruiters like to work with people they know won't waste their time.