From my experience on ICE trains, I'm usually better off creating a mobile hotspot from my (5G-capable) phone with a Telekom contract compared to using the wifi.

From what I've heard, the websites are pretty good at getting money if it's possible, because they've seen all cases and only make a profit if they do win. Disadvantage is that they take 30+% of the compensation.

To be honest, I think you can forget about finding a one-way rental. Alternatively, you could rent a bike in Amsterdam and take a train back to return it. But even then, in my experience it's pretty much impossible to find bike rental that are not either city bikes or, in mountainous areas, (steeply priced) mountain bikes for day rentals. Realistically, your best and cheapest option would be to fly to Amsterdam (assuming youi're coming from CA) with your own bike as special luggage and use that.

It really depends on the card in question and one should read the terms. For example, in the case of the card I have, it doesn't matter whether the travel was paid for the card, with the exception of car insure: in that specific rate, the full rental must be paid for with only that card.

Might be worth using the airline support channels by taking the $500 receipt, saying that this is all you were given after repeated request, and noting the discrepancy to the $2300 charge. Then explain that apparantly you've been overcharged and would like your money back. Perhaps asking for money based on the receipt makes them correct the invoice, after all, or you even get the money back. As long as you describe things honestly, I don't see how this should be illegal. Note that this is less drastic than going for a CC chargeback directly.

@Muzer Not that I'm aware of, unfortunately. You could buy a flexible ticket well ahead in the future and use the free cancellation it offers.

Absolutely a scam. Sorry for you loss of $2k.

United just seems to have a crappy IT system. Had a similar issue with a flight booked at Swiss, where the international leg was premium economy and included two bags, which extended to the US domestic United leg. United personnel at the airport admitted that the second bag should be free, but were unable to waive the charge. Had to pay and apply for reimbursement.

I've gotten a saver fare about 10 minutes before departure. That was a mostly empty TGV between Stuttgart and Karlsruhe, and the discount was only a few Euros for this short distance, but it was still a saver fare.