Individual airlines may insist on sight of return/onward ticket or 'some sort of visa'. There is a very recent report of a member being 'pinged', stopped at the departure gate and asked to provide this information. The reason given was that he had checked-in online. I have been stopped at the departure gate and denied boarding. I was told that although I had checked-in manually for my previous flight leg with an airport agent, they should have insisted upon sight of my documentation before checking me in.