Originally Posted by
xobile
I think it's important to note that it is not always the first carrier's allowance that applies, but if applicable, the marketing carrier. In this case, if you are buying on the UA website and the ticket comes from UA, the UA baggage allowance would apply, as they are the marketing carrier.
No in the quoted instances the ticket is being booked on the United website and issued by UA. The difference is that UK is a codeshare and AI is interline. In both cases UA is the marketing carrier but the allowances are different (UA's allowance for UK, AI's allowance for AI).