As far as the best temperature to drink wine goes. The guest is not always right, but they are always the guest.
If they want to drink their white wine warm and their red wine cold, just smile and help them do it.
If they want to have ice cubes for their white wine in the summer, don’t tell them the melting ice cubes will water down and change the taste of the wine, just give them ice.
(That is unless you have some of the reusable ice cubes or stones from the freezer at your establishment.)