If I find round trip airfare is cheaper than the one way to my destination, can II just buy the roundtrip and dont show up for return trip?
Yes, that's a common hack. There's another common hack based on the weird fact that sometimes the further you fly, the cheaper it is, IF you don't do it non-stop. Say you want to fly from Seattle to Chicago, and a ticket costs $600. But you may find that if you fly from Seattle to New York with a stop in Chicago, it only costs $500. So you buy the ticket to New York and just get off the plane in Chicago. (This doesn't work if you've checked luggage though, because it will still end up in New York.)
Yes. They won't track you down and force you to get on the plane.
Yes, but it's more unlikely these days, as airlines increasingly market flights individually, so often one way is the same price on its own as it is with a return attached.
You can, BUT don't even think about doing it on the outward trip. If you miss any part of a round-trip journey except the very last, they will cancel all the parts that follow.
Do it all the time. As you need a exit ticket. From most Countries. Or can not board international flights
Yes Make sure you do turn up for the outward leg - otherwise the return may be cancelled
yes. I have
will I still get my travel miles?
Yes, just be sure to not check in any luggage, for two reasons. 1) Your luggage will not get off the plan with you, and you'll end up leaving your luggage behind. 2) Since your luggage is on the plane and you are not, the plane will not be able to take off unless all passengers with checked-in luggage are accounted for. You will end up causing the plane to sit on the tarmac for hours while the airlines searches for you. If they don't find you, then they'll have remove the contents from the plane until they find your luggage.