won't play a lot of our DVD's

We purchased two of these units about a year ago. Both have difficulty playing DVD's that our other two Sony DVD players have no problem with. So the kids wind up watching "our set" because they can't play their work out videos and other store bought videos on their Samsung unis in their rooms. (forget playing DVD's you make yourself! Never could play them.) I contacted Samsung and they had me reset the unit, no help. I already cleaned the lens, no help. The solution was for me to send in the unit for $85 worth of service! And I have two of them! Brand new they're like $100. $99 too much. What good is a DVD player that can't play or has trouble playing at least 1/2 the DVD's you put in, some brand new out of the box! And what good is having them serviced and getting them "running like new" when they were like this brand new out of the box?! Should have called earlier, they didn't get much use for a long time but now the kids are a little older and prefer to hang out in their rooms more. Live and learn.