Used drums

My wife has been interested in playing the drums. I beleive that playing any instrument enriches our life. Today, we went to a musical instrument store and bought a reasonable used electronic drums. As soon as getting home, she set up and played the drums happily. In that time, a miserable thing happend. While My 7-year-old son played the drums, one of the tams didn't make sound at all. Maybe it is broken...I will take the drums to the store and have it fixed or refund.