... for me, the issue was rust under the rear wheel arch covers, where water got trapped.
I did rust proof - a messy job - but i'm not sure it made a huge difference. It seems to be where you cannot see as much as where you can...
Definitely worth consideration though.
Tricky as it is and a hassle, but ... if a third party questions the tyres ( and safety ? ) of the tyres, I'd be tempted to return them?
Which may of course not be entirely practical. I wonder if they think all the tyres are 'bad' and how they might have become so?
Best wishes.
+1
I used one well know product ( cannot remember the name ) that used a cleaning towel and then a sealing towel.
Terrible. The cleaning left a murky film. Spent ages trying to get it off.
Another product that just seals and cleans in one, works well. But, as Malc says, these things don't last.
Other milk cartons also do it now. I generally need a bath and the kitchen needs a deep-clean, after doing-battle with one of these...
Milk; mug: milk second, tea cup: milk first. Though I generally let my butler decide.