I could try to make puns about this but they would probably miss important elements as well

Well that's not a good business model.

You have to check the ratings about the seller and look at the feedback people have given that seller.

WOW!! YOU'VE GOT REAL PROBLEMS!!!

every problem is a real problem.

its not nice to invalidate another person's bad experience just because someone else had it worse

I think the company is also missing the fact that this may not be good for their ratings... but btw OP, is there any way you can contact the manager/supervisor/person-in-charge, Or can you get the pieces from another company??

Keep making them send you kits until you finally have all you need.

I recently bought a book that had blank pages where the index should be. I called the publisher and they sent me a new copy!

Sorry, that sucks. But make them keep doing it until they do it right. Good luck

Ask if they can just send that specific part instead of returning the kit you have and waiting for them to get it and waiting again for them to send a new one.