I wasn’t aware that it was so skewed to the customer’s benefit, but I’m sure online is the future, even if the bricks and mortar stores are retained for display and demo purposes.
I think both online/brick and mortar are still necessary tbh. Its v hard to buy certain stuff online. Expensive hifi equipment that you can't hear before it turns up on your doorstep is definitely one of them (as OP discovered, and also brings this thread nicely back on topic) but there are many others too.
Not all retailers say this in their terms though.
They can put whatever they want in their terms, but the legislation will always take priority over their T+Cs. As a customer I am perfectly entitled to return a product I bought online after 13 days because it is blue and I don't like blue things on a tuesday. The law simply doesn't care how ridiculous my reasons for return are, its so badly thought out!
In practise there's very few people that abuse return systems like this and its often a drop in the bucket for big retailers. But its a major kick in the teeth for smaller sellers. Especially for niche high value products. As you can see an open box drops the price by a lot for this sort of stuff......