British airlines selling AA tickets? International flight
 

All the One World airlines sell each others tickets - Sometimes code shares sometimes not (Same with Star Alliance, Sky Team, etc)

So this is a fairly ordinary thing? No unexpected downsides that I'm not seeing?

It's cheaper than that AA is selling flights for those same days. That's why I'm wondering.

Yes, fairly normal. If you find that same flight via AA, it will likely say something to the effect of "operated by British Airways" or vice versa...

My upcoming flight from Belgrade to Paris (on route to SF) is an Air Serbia flight but purchased through Air France due to their partnership.

First, what are the flight numbers? If it is a very high number like BA5xxx, then it is an AA metal.
You are only looking at the face value and not the opportunity cost.
If all the flights operate as scheduled, there is little difference between ticket bought from AA as the marketing carrier or BA.
However, there is a big difference when something goes wrong.

When there is a major delays before you start the trip or cancellation, the marketing carrier who sold you the ticket, not the operating carrier (the one that owns the metal), is responsible for providing you with an alternative. In my experience, the marketing carrier tries first to use their equipment as much as possible in giving you a replacement. I had a KLM flight ticket sold by Delta. KLM cancelled the flight. KLM said it was not their problem anymore and told me to talk to Delta.

If you decide to cancel your flight, if your ticket generates a time limited credit after cancellation minus the change fee, the marketing carrier retains the money. In your case BA. That credit is only usable in the future on flights marketed by BA.

That is more or less what I'm worried about, Greg. If it all goes well, great. If not, I don't know how BA is customer service wise--it's not an airline that I have much chance to use.

I'm not sure about flight numbers-- maybe this will show what I'm looking at--

https://www.google.com/flights?hl=en...sp:2.USD.31233

Many airlines sell each other's tickets. When you get to Seatac for your flight to London, on the reader board you'll see the (BA-operated) flight carrying flight numbers for BA, American, Iberia and Finnair. (Those airlines adopted a big revenue-sharing scheme some years ago.) The prices are different because the seats AA sells on the BA flights carry slightly different fare rules than the ones sold by BA. In 99%+ of the time the differences are totally invisible to the passenger. And no, you're not going to get bumped or otherwise hassled; the seat's been sold to you when you buy it online.

You will need a BA boarding pass, which will have a different record locator (the six-letter/number confirmation code) because the one you'll get from AA is for AA's system, which is different from BA's. You'll check in at the BA desk where they'll do a passport check and will give you your boarding pass, then off you go.

Once you've bought the ticket, you can go on line (or worst case, phone AA) and get your BA confirmation codes. You can use these on BA's website 24 hours before the flight (in the case of connecting flights, such as SEA-LHR-AMS, 24 hours before the SEA-LHR one) and pick seats for free; earlier than that and you'll have to pay a fee to pick seats. The whole thing can sound complicated, but it's really not. Millions of flyers do this with no problems whatsoever.

In the event your flights are NOT SEA-LHR-AMS, but instead involve a domestic leg on AA before the transatlantic one (doubtful) then you'd check in at AA. You always check in with the operating airline, not necessarily the one that sold you the ticket.

Amsterdam at that time of year is magical.