There is no reason that dance music should not be played at the correct Tempo. Unfortunately we have bands that play the music to suit the vocalist and not to suit the dancers. They cant read music Therein lies the problem. Bands playing music to dance to is being played by people who cant dance a step. If playing canned music the person selecting the music must have the above mentioned knowledge. If I were the selector and choosing a group I would give a list of the correct Tempos. If in return I got a blank look. I would look elsewhere.
Disks. Not all disks are suitable. There are some cheap useless music out there. Go for the established orchestras. You'll pay more, but its worth it . On the back you should see written the track number. and the number of BPM
It would look like this. 3. Chariots of Fire. Rumba. BPM 25. Time 2.41.
Time is the length the disk runs if played right through.
If this were a competition the dancing time would be 1 minute 30 seconds but could go for 2 minutes or until the judges are satisfied.