I'm not sure which airports this hack is for but in my experience in US and Europe the opposite is true. A one-way ticket often costs almost as much as a round

I'm not sure which airports this hack is for but in my experience in US and Europe the opposite is true. A one-way ticket often costs almost as much as a round trip ticket, I never understood why. Also the origin matters a lot. A trip between A and B could cost less if you eventually return to A rather than B.