To high output level in the FOH mixer from the DJ mixer

Hello, I work as a stage manager on more festivals and I'am also a dj and producer and a soundtehnician. The most comon issue that I have on events is when the Sound Tehnician is connecting the Pioneer DJ mixer to the FOH mixer(dosen't matter witch model 900,900nxs2, v10, A9) The signal is to high, and probably most of them are using DIY's to lower the signal and have headroom for adjust the sound. What can I do the aviod the DIY's and how can we mount the DJM mixer to avoid this kind of issues?? Any suggestions?