At about seven of ten houses, that I inspect in Whatcom County and Bellingham, there is at least one sliding glass door. Often these can be difficult to operate or test. Sometimes a seller will have a keyed lock on the lower track, that keeps it in a stationary position. In that case, it may not be possible to check the door. Other times, you have to fish a wood stick or similar bar out of the track, security measures.
Once the door is free, so it can be tested, I often find that the latch is out of adjustment. In what could have been an embarrassing situation, years back, I was testing a sliding door here in Bellingham at a condo and, when I shut it while standing outside, it locked me out of the residence on its own. Thankfully, the front door was still unlocked or I would have had to have called the agent to get back in.
As to common problems, sometimes the thing is stiff, so it is all your life is worth to drag it on the track. Other times you have to lift up on the door to get it to latch, endlessly twiddle with the latch or, finally, give up and simply put the stick back in the track. At the door shown below, the latch operated but it was out of alignment so, even when it was in the up or locked position, it did not engage at the other side. Therefore, the door was not secure even when it looked like it was locked. The good news is that, often, the adjustments are not so hard to accomplish.