Originally Posted by
milehighj
....They could allow a conditional check-in and seat selection, with the stipulation that the passenger is still required to go to the counter for a document check.
Yeah, they do. For example, when you book WCHR, you can do the check-in, though won't get a boarding pass.
For Visa/immigration items, they may want to be a bit more strict.
Originally Posted by
milehighj
Out of curiosity, does anyone know what a carrier would do if a passenger holding a one-way ticket intends to exit the destination country by land border?
You will need to show "something", that lets you leave the country. A ticket on another airline, an online bus-ticket, or whatever. And for some countries, a permissive VOA mechanism in the arrival country could be enough.