Buying Theme Park Tickets for Disney

I have been to the parks several times and waiting in line behind someone with problems with their tickets and found out that they had purchased the tickets from someone for cash. The people were told that the tickets were good for one day only. It turns out that Disney and Universal tickets are sometimes sold by individuals who are not certified vendors for the theme parks. The certified vendors will have a license to sell the theme park tickets so be careful buying tickets for cash. Bottom line is to buy your tickets online before getting to the parks or buy when you get to the parks. You do not want to ruin your vacation while trying to save a few dollars and in the end you may be spending even more.