Hello GP,
For me, it's normal to clean them ''gently ' when the weapons were really bad preserved: lot of red rust of all black rust too,
I think we have to !
Not with a mechanic sander and 80 grain as I already saw
Sure it's a disaster!
Nothing better than an example:
Not talking about money but this all rusty shamshir I have per example,
bought less than 80 Euros couldn't stay like that...
now I can sell it for a fair price but I prefer to collect...
Experience, passion and good skills helps too,
I worked in antique furnitures and collect blades since more than 20 years
it helps ! , half of my garage full of stuff like ferric acid , choji oil, sand stones.
It's like a second job !
Sure if its too damaged or costs an arm and a leg,
better consult a specialist ( difficult to find for japanese swords per example and expensive as David said )
or leave it like that !