Ok.

I watch these perfect videos by perfect builders and perfect CAD/CNC techniques by the factory. Why what could ever go wrong ?

Well, on another website I read of one fellow who had to undo the wing of his quick build kit and re do it to get it right.

Without mentioning any specific planes or manufacturers, has anyone received a quick build kit and had to correct a manufacturing/fabrication/assembly defect? If so, what was it. I realize parts occasionally may be missing, and I am not really asking about that. I am more curious if things like wavy fabric covering, or bowed out metal skins, crooked rivets, etc are seen ?

Only experience thus far is with Rans QB kit. The only holes we've had to "adjust" so far are a handful of those that come pre-punched that attach the firewall to the airframe. And the manual says you'll have to do that. The level of detail of work you don't have to do is pretty amazing really, not to say that it isn't still a pretty serious project. What is nice is that the manual will instruct you to go "find item xyz and install it," where others will say "go get yourself a piece of (insert material here) and fabricate item xyz". Very thoughtful for those of us without a sheet metal or machine shop in the corner.

Customer service is good, they are busy and sometimes a little slow which is understandable. The boss man is accessible for calls also, which is nice and sometimes necessary.

I am far from an expert, but the covering job sure looks good to me too.

Hope that answer helps.