Last month I booked a ticket with United - SIN-NRT-EWR with the first segment operated by Air Japan as an ANA flight in economy and the second segment operated by United in premium economy and I was not asked for my credit card at check-in in Singapore.

I had bigger problems though - I could not select a seat on ANA's website despite having the ANA confirmation number, nor could I select a seat on Air Japan's website. Tried calling ANA customer service and Air Japan. Air Japan told me I had to call ANA since it was their flight and just operated by Air Japan. ANA customer service said they couldn't assign a seat and that could only be done at the airport. At the airport I couldn't use the kiosk to check-in, I had to go to a representative. I asked the woman if there were any aisle or window seats available as I didn't want a middle and she ignored me. Printed a boarding pass with a middle seat in the very last row of economy. I then asked if this was an aisle or window seat and she said "I assigned you a middle in the very last row". I again asked if she could please give me a window or aisle closer to the front of economy and she rolled her eyes and assigned me an aisle in the third row of economy. I thanked her and walked away as quick as possible before she changed her mind.