This comes up every year. Here are some past threads about Sample Lessons (there are lots more!):
http://talk.qa.collegeconfidential.com/music-major/1200032-please-demystify-the-sample-lesson-situation.html
http://talk.qa.collegeconfidential.com/music-major/2016860-trial-lessons-campus-visit.html
http://talk.qa.collegeconfidential.com/music-major/904682-sample-lessons.html
http://talk.qa.collegeconfidential.com/music-major/850405-when-to-schedule-sample-lessons.html
http://talk.qa.collegeconfidential.com/music-major/1470254-sample-lessons-with-more-than-1-teacher.html
http://talk.qa.collegeconfidential.com/music-major/1500003-sample-lessons.html
http://talk.qa.collegeconfidential.com/music-major/850220-contacting-teachers-for-sample-lessons.html
http://talk.qa.collegeconfidential.com/music-major/771852-payment-for-sample-lessons.html
http://talk.qa.collegeconfidential.com/music-major/559919-sample-lessons-which-teacher.html
http://talk.qa.collegeconfidential.com/music-major/1283509-please-explain-more-about-trial-lessons-to-me.html