I have had 8 iPads total, new and warranty replacements, regular and mini (over all gens) and have never seen dust under the screen.
Are you breaking out the ol' electron microscope or something???
Seriously though, I'd get the best one you can live with and just keep it... I hope it works out for you!
Snide remarks with 'rolleyes' are not helpful in any matter, let alone this, and I can sympathise with the OP.
These issues are widely reported, even by regular blogs & media tech testers everywhere.
I'm certainly no fuss ar$e and yet have had the following issues;
64gb cell retina mini.
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1st ipad mini retina - piece of red thread under screen (long enough to make the letter 's') 4 apple staff poking at it. exchanged;
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2nd (replacement) 2 pieces of debris under screen, dead pixel and backlight bleed, scratch under screen. genius saw it before he even gave it me and said to me it wasn't acceptable! exchanged;
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3rd (replacement) duff serial problem, faulty speaker, loose power button, scratch on top screen, yellow to blue tint. exchanged;
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4th (replacement) yellow to blue tint (genuis observed and immediately noted it) awaiting exchange.
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5th ordered.
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Great quality hey?
Absolute shambles. Spent thousands over the years on apple equipment, never had this trouble before.
So yes, actually, it is a fiasco for quite a few folks. There's quite a few largish batches of poor QC. End of story.
For the record, I've spent thousands too over the years with apple, had previous ipads etc, only now has this happened.
YMMV