A GS will have the 2.0. (I had one). I know nothing of the 1.8, but I know the 2.0 is prone to noisy lifters. Mine sounded horrible when the engine was cold, but when it warmed up, it purred. I'm not sure what mechanical implications come from being noisy (if lift is compromised) but the car ran great despite the noise on cold mornings.
If the timing belt has been changed, that's good...BUT....A friend and I changed the belt on mine, and it broke about a year later. Not sure if it was a shoddy belt, or if we kinked it sometime during the install. It had 15K miles on it, maximum. How long it lasts depends on who made it and who installed it.
Be thankful of the 5-speed, but make sure it shifts into 2nd gear without protest. My 2nd gear synchro was starting to 'complain' when I sold it...something that doesn't often get better on its own.
The only other thing I can think of that's an inherent problem with the 2.0 is the idle air control valve. When they get dirty, they sometimes have a hard time deciding where idle is. Sometimes mine would bounce between 900 and 1500 until it got fully warmed up. And, if I ever unhooked the battery, it would completely forget how to idle and would die at stoplights for a few miles, and finally operated normally. Take it for a test drive to look for any signs of this. Sometimes this can be fixed with a throttle body cleaning...other times it requires a new IACV.
Taking all this into account, I'd say $400 is a pretty good deal.