Airline Ticketing question

That depends on the airline. Read the fine print and confirm with the airline. Some airlines state that they can request to see the card at check-in.

I have been asked to show my credit card at check-in.

Ethiopian Airlines specifically states to bring the card you used to purchase the tickets.

You may run into an additional issue, depending on who the ticket is purchased from. When I booked tickets for my sons three years ago on one of the consolidators, I used a card in my name that they did not yet have in their name. I was immediately contacted by the consolidator to provide some id for me (IIRC, a photocopy of my driver's license was sufficient) and short e-mail statement regarding this so they could put the purchase itself through.

To answer the simple question posed about buying a round trip ticket to BCN, no, he will not need your credit card. Just a passport. The credit card and train ticket is common through out most of Europe but in those cases the name is not important.

Thank you all for the responses. He will be booked on Delta as that will be the easiest routing from where we live in Idaho to BCN. I will probably go ahead and use the card he is a signer on even tho it is not the card with FFpoints. It certainly would be no problem to show up at the local airport with him if the CC needed to be shown, but way more difficult from the BCN when he returns home!

British Airways website says this

If you have booked directly with British Airways, either through ba.com or a British Airways Telephone Sales office, and you paid with your debit/ credit card you must present that debit/ credit card at check-in. This is to assist the check-in process and to provide debit/ credit card verification.
When using a Self-Service Check-in kiosk, simply insert your credit card (for identification purposes only) to begin the check-in process.

When I have checked in for international Delta flights from Seattle, I'm sure started by sliding my passport through the automated kiosk reader, and did not show a credit card.

Delta has never required me to show the CC that I have paid for tickets with. Fly them all the time. In order to do self check-in you can scan your CC or passport for them to locate your itinerary, or you can enter the itinerary number. I often pay for tickets for my daughter, grandkids, etc. and they live in another state and do not even know what card I used.... you just need your ID.

We fly on Delta/Air France several times a year and have never had to show our credit card. I'd go for it because you'll get double miles and he'll have priority boarding.

Pam, I think you are wise to use the card your nephew can sign on. Over the years, I've seen numerous reports on flyertalk where individuals have been required to present their credit card at the airport for check-in. For example, here is a recent report where a Delta passenger was required to present card for check-in.
http://www.flyertalk.com/forum/delta-air-lines-skymiles/1550519-no-olci-must-present-card.html

It is certainly not likely to happen, but it does happen. I don't know what triggers it (suspect they are concerned about fraud), but as I mentioned previously, it has happened to me when traveling on business and I've seen notices about it on airline ticket confirmations.

I again appreciate the responses. I had not seen the FlyerTalk thread altho I had looked on the Air Travel forum on TA after I posted here and saw similar tales of woe. Yikes.

The nephew in question traveled to Italy with his Mom and Dad, brother and me last May so he has some experience but not sure he could figure this out if it happens from the BCN end. The airport we fly from does not have check in kiosks so it's either the agent or online. I got chewed out my last time thru for doing on line check in for an International flight and for not going to the desk so he could put my passport verification in. The airport is small enough that the desk agent closes the desk and becomes the gate agent.

I think we will go with the card he signs on just to mitigate any potential issues.

It is largely a fraud issue, and there are apparently a few destinations, particularly in Africa, where the is bad enough that everyone is required to show the card used for that route on check-in.