Some people do like to moan about pretty much anything, don't they?

My experience is that appropriate background music, well chosen and played at a sensible volume, often results in people coming up to the desk and asking what they're hearing. It can sell records by hard-pressed artists. It can subtly advertise future gigs. It can (shock, horror) provide a nice social atmosphere where people can talk. Many may feel inhibited about doing that if a bunch of musicians are having a tune session - since many live in fear of the no-fun shushers and tut-tutters at any gig involving folkies.

Rule of thumb (or perhaps ear) is that you should be able to comfortably talk over it - i.e. not need to shout. Same applies to restaurants . . . where personally I hate having live music as I feel very rude having a conversation and eating, even though that's what the place is for.