I certainly get where you are coming from, it's much like a naming convention, very useful when building databases things need to be consistent in order to make sense down the road when you go to use things you've setup.
But getting folks to change their habits is pretty tough and some are not really that savy when it comes to computers so that adds more to the pile.
I for one will try to preface my for sale listing with maybe just the
USA: blah blah super duper cutter with unobtainium steel and the like....
So for everyone scanning through the pages of for sale items, the
USA: will be an indicator that you can browse but most likely not be able to buy from this person. It would be a simple way to state it.
Which brings up a pet peeve of mine, I have several so I'll not bore you with the others

, but when a person's for sale thread has all the stuff sold, it would be Nice if they would EDIT the title of the thread with it right in the beginning, example;
SOLD: blah blah blah best knife ever...
it's a similar thing, you go and read the forsale post only to see you've wasted your time, now there are those that will edit the title but put Sold at the end of the listing, while not a big deal it still irks me, see, I'm easily irk'd lol

G2