Your friend's only error may be in the choice of DVD blanks that were used. Commercial CDs/DVDs are mechanically stamped creating tiny pits on the media that cause the "read" lasers to either reflect or not. "Burneed" discs on the other hand use "write" lasers to change the color of a dye on the disc so that the read lasers will either reflect or not. The fly in this ointment is not all CDs/DVDs are equal and variations in the reflective layer of the disc, the frequency and power of the "write" lasers, the dyes used, the frequency and power of the "read" lasers, dust on the "read" lenses, even the age of the disc can and will effect whether a given device can read any specific disc.
A few years ago there were published estimates that by and large and one the average a given burned CD/DVD could be read on ~70% of players. Because there are so many different read and write lasers crammed into a computer disc drive they tend to fail to read a given burned disc most often, but the simpler drives used in commercial CD/DVD players can be among the 30% if devices that fail reading a given disc.
