If I order some shoes from Amazon, I find them uncomfortable, and I return them for a full refund causing Amazon to incur a loss - have I been "subsidised" by other customers?
Personally I would say if Amazon makes a profit selling you a book and makes a loss shipping me some shoes which I return, the loss was paid by Amazon, not by you.
The comparison is more apt if you gained something (because the bandwidth user gets a product out of it), say by having worn the shoes for a day and doing this every day so you get free shoes for life. Then, yes, it's pretty clear the paying customers are the ones footing your bill
Personally I would say if Amazon makes a profit selling you a book and makes a loss shipping me some shoes which I return, the loss was paid by Amazon, not by you.