Kurt
It's just recently that i controls all the kits i buy.
On the last 12 kits , two were missing a small sprue: the one with two sprockets in a Meng kit and a plastic grill in a Frog 7 by Trumpeter.

I now just hopes that my +200 kits are full of the parts...

Well, let me tell you my story.

I have about 500+ kits in my stash and until a year ago I was living blissfully unaware that sprues might be missing from a kit. Then I stumbled on some forums on two distinct people complaining about missing a sprue on a Takom kit so that intrigued me. I had bought a Takom kit that day (the ZSU SPAAG) and I opened it right away and lo and behold I was missing the rubber wheel part sprues. All 4 of them.

Fortunately it was from my LHS so I went back, they didn't have a replacement but they refunded me.
Since that moment on I started controlling all the kits I'm buying. And what happened next?

Well another Takom kit (ltPsv 90 Marksman SPAAG) showed up missing all the track links. Again I went back with the kit to the LHS. This time they had a second kit in storage but surprise, surprise, that one was also missing the track links. They wrote to the supplier who promptly sent back some track links, unfortunately the wrong kind. They wrote back but this time no reply yet. Still waiting on that (4 months have passes by).

But the idea is that I was fortunate that those were kits from my LHS and they are really great in how they handled the issue. If it was from an online, foreign order that would probably had been more complicate.

Anyway, I'm now diligently check every kit. Not just Takom. Although I got to see another customer in the LHS complaining that a Mark I Takom kit was missing some sprue. And considering how many people I see online complaining on Takom kits missing something it looks like they really have a bad QA issue.

I really hope that the couple hundred kits I already had in the stash unchecked are fine

Yes I have learnt that lesson, always go through the box as soon as you get it. That is all well and good with some instructions as they have had all the parts shown.

I have bought studio scale Star Wars kits over $600 and they don't show you all the parts and you only find out once your building this that its missing parts. They also do limited runs so when they done their done. Its a gamble unless you get one of the good/honest guys that will go back and recast a part for you. Some don't believe you or some just say sorry to bad.

What worse if in good faith you sell on a kit ( that you think is fine) and the next person says its missing a part it gets very tricky. Even though I have a few studio scale kits I would not sell them on in fear of them missing parts.

I don't think I'm qualified enough to speak (I started less than 2 years ago and have less than 20 unbuilt kit) but I always buy from LHS and check the kit thoroughly before leaving. Never had a missing part or sprue.