$13,500 staircase and we get grade E timber.

That's fit for purpose. Good luck with your dispute.

Unless your stair treads or exposed stringers look like this (which i assume they dont), the timber is fine.

Can you explain what you think is wrong here?

I think you've gone off the reservation to be honest. I'm fairly certain this piece of wood isnt considered load bearing, the stringers are. Get all the classification testing you want, personally i think youre wasting your money. You'd have been better off having gotten an independant inspector for each stage, which ive noticed you dont seem to have base don your other posts.

Out of curiosity, did you check everyone one of your framing members was stamped and certified as structural timber? Like every single one? Cos i have news for you, three's so many chippies out there that will use non structural timber where they should. Happy hunting.

agree with ponzutwo, looks pretty normal, visual defects are pretty common and don’t make it defective automatically. Timber can be F graded visually or machine graded MGP, for studs and other structural applications.

This has some useful info on the size of defects allowed:

https://www.outdoorstructures.com.au/timber-grading.php

I think you’d get more damage removing it for no reason. This is standard to put this defect somewhere it won’t be seen.

The best prize fighters do it, so they can't be wrong.
Thanks for your asinine input.

Thank you for your ''input" once again, but It's my money and I can do as I please. I don' think I've seen a more ignorant response, concerning professional boxing and the trade. Of which you clearly know neither.
Clearly, a self proclaimed arm chair expert which has difficulty in comprehension and constructing an English statement. Throwing barbs and having a sense of entitlement, as what I posted must have hit home hard.
We love exposing charlatans like you and once less person that's taken for a ride by your ilk, Is a job well done.

Stick to your Irrelevant commentary even if your feelings were hurt. I cant help that. It's untoward and best left in your feeble minded echo chambers.
I smell mangina and keyboard warrior and so before you start lactating, I best leave you at your own peril.
Dont waste my precious time, I've had my fun with you.
Have a good day

Assuming underneath the stairs isnt exposed (its a storage cupboard or void) then I dont see any issue with that piece of timber. You'll forget its there and visitors will never know. I doubt that knot would have much impact on the overall strength of that tread.