What exactly is the problem? There's no point in naming & shaming a retailer. Sound & Vision is perfectly within its legal rights to refuse a return when there's nothing wrong with the receiver itself.
According to Sale of Goods Act, If there is nothing wrong with the item, you don’t have the legal right to return it.
If you describe your problem, maybe some members can help you out. In what way is Plex media not compatible with Yamaha receiver? What's the receiver's model number?
You are right! The shop is not obligated to give a refund...
But I did explain what I wanted the amp for (To have it connected to a mac running plex media server) but the remote that came with the amp conflicted with plex,
I changed the IR id on the amp which still conflicted but with a different commad,
I rang the shop and was told to use the app on the iphone instead, or have a store credit, but we only sell Yamaha/Onkyo they also said they would contact Yamaha support, which I also did and the advice was to use the scene button to cahnge inputs...