The person that comes to a forum is many times having issues. This tends to make forums appear to show more issues than are common.
The same thing happens in Astronomy. A manufacturer makes a fine piece of equipment, excellence in engineering. But a very few, have an issue of some sort and rather than working it out, they blast the internet with their dissatisfaction. They do this on every forum then can find, I assume to vent their frustration or to make the manufacturer pay!

I have seen this many times, an otherwise excellent product is made to seem less than stellar, which is not true.
I have said this before, but worth repeating. DJI sells a lot of Phantoms, lots! If there was a true BIG problem with their products, there would be hundreds of post a day looking for answers. But, as you can see, that is truly not the case.
If you have thousands of units out there and you only see a few problems showing up each week, then that is not a bad situation. If 1% were having problems, we should see 10 for every thousand, with these problems. That would equate to a lot of people, which we don't seem to see on line complaining.The chances are that 1-3% of all products will have an issue, no matter what it is. That is just reality.
The other idea brought up about returns and reselling of the returned items. This too happens all the time with everything on the internet. DJI, sends out refurbished for repairs, some sell them on line too I have heard. But if you got 4 as someone said, before they got a good one. Could it not be possible that these same defective units have been sent out before, maybe a few times. What happens to those that are returned to a vendor, do they return them to DJI for repairs or what?
These craft are much more reliable that any RC that I have owned in the last 40+ years, better range and more responsive. To me it is amazing that they can pack so much I so small a craft.