To get back on thread and try to answer the OP's question why dont they play decent music at hi fi shows ? you need to look at it from the demonstrators viewpoint.
They are stood around for a few days sometimes in a near empty room so they play what they want to hear most of the time unless asked to play a certain track etc. therefore in general its the music that they like or are trying thats being played not what the potential customer wants to hear.
The other point that has been raised is the fact that dem room clashes with music levels in some cases overlapping into another room does at times mean that levels are kept down as to not interfere with other dems close by.
The worst shows are in hotels IMHO bloody ridiculous sizes with dreadful acoustics....Bristol springs to mind which i now refuse to attend.
A refreshing thing happened in one dem room at the last show i attended which made me think that ALL demonstrators should maybe consider......as we entered the room he gave us an ipad and asked us to choose a track that we wanted to hear and then passed the remote for the volume control - nice touch.
On the flip side in particular room they had set up two pairs of speakers with two systems one was set along the north wall which when entering were being played with some obscure tecno stuff at silly volume levels and another pair with a similar system at right angles along the wall to the west.
I asked several times if we could hear the other speakers which i was and am still interested in purchasing at some point to be played to which the guy totally ignored my request.
In the end as the guy seemed uninterested in my request and the room was near empty i repositioned the seats (approx a dozen) to face towards the west wall now facing the speakers that i wished to hear and asked for him to play an LP that i had picked from the variety that he had.
he seemed rather taken aback at first but quickly helped us move chairs and realised that its not about what he wanted but about what a potential customer wants.
i and many others enjoyed this configeration more instead of the first one that we were listening to - JOB DONE