[russum]

Couldn't you get the "Round trip, SFO-PVG: $700" ticket and then use it only one way PVG-SFO?

[saryant]

If you skip any segment of an itinerary, all remaining segments will be cancelled. In airline parlance, "flight coupons must be used in sequence."

[toomuchtodo]

Which is why you look for the flights DEPART->ARIVE->DON'T CARE and you just need make the second leg.

Don't do this often if you care about your frequent flier miles though.

[thaumasiotes]

Can you? I was told that airline tickets get canceled if you fail to complete a leg of the itinerary.

[rajivm]

Yes, you are correct, for many airlines the remainder of the itinerary will be canceled if you miss a leg (and don't replace it). However, in some cases, it is possible to cancel a leg in advance (paying any change/cancellation penalty), possibly resulting in a lower fare...