A friend of mine booked a one way ticket YUL-TLV, they didn't let here board the flight until she booked a return, is this a law or something?
Not a law, but some agents will make you problems. YMMV
So booking a refundable one way for the way back is the way to go?...
Yes. ive done it multiple times. Only airline to give me problems was LOT.
Now, how can I know if a ticket is fully refundable?Also would a hold with AA be enough?
Yes. That should be fine
I should just put a flight on hold with AA and print out a copy of the reservation, and show it to the agent? Is that enough, or will they check if I have a actual valid ticket?
Printout is enough. Or sometimes just showing on you phone
Who gave problems?
Don't know, that dude is flying now...
Experience: To Israel was booked thru UA and they warned me that "Israel" would want to see a departure ticket (which I had booked thru AA). No one asked any questions other than the regular passport control - how long you staying for?
I have a OW booked with no return ticket yet. Will they give me problems?