How much is "quite a lot" (wonk) ?
My experience with numerous brands, has been that you can be lucky you get a "straight" kite, but they can often be 1 or 2 inches off to one side.
Meaning, you have to adjust the knots on or the other one rear line (or at the kite)
This is normal for all brands, and nothing you can do about it.
But are we talking such an amount that it does not fly right and turn okay ?
That is another issue then...
I've only experienced that once, 10 years ago, where a kite was sewn so bad that it twisted so much - that even when it flew only on the frontlines, it turned quite heavily
Otherwise all I've seen has just been a matter of adjusting the rear lines a bit one way or the other, so they fly perfectly straight when sheeted in (and sheeted out they fly okay).
Is this what we are talking about ?
Or a way more disatrous amount of uneveness, so not usable at all ?
How much/fast do they turn with fully slack rearlines ? (first test)
And how much do you have to adjust the rearlines till it flies straight with tight rearlines ? (second test)
I've had many kite that were bulls-eye, but also some that needed one or two inches rearline adjustment as said - which is pretty normal
PS: I am not talking about line stretch or lenght errors of course - but the factual measurement from bar end to kite !