I have bought my son a cheap Chinese quad two years ago. There has been three problems with it. First was just the bolts. Solution: Make sure ALL bolts are tight before riding! Also they will work loose so Loctite them or keep checking them.
Second the clutch sucks! But then again that may be cuz it hauls my 225# butt around. Best way to fix this is to get the friction plates for a Honda XR70. Only 30 bucks OTD.
The third thing is it still sucks going up hills. I will probably change the sprockets to help this out. I know I will lose some of the top end. But Really for a $900 quad I couldnt be happier. If something does go seriously wrong then Oh Well. I have gotten my moneys worth.
In general I would by another one. I have had fun on this little thing throwing it around!!. It has been rolled, run out of oil, and jumped many times. Although it is about time to get some tires. I still think for the money it is a good choice.