Today I received this Omega Seamaster 300M bought from an online store, where it was listed as “used.”
However, when shining a light on it, I noticed several scratches.
Do you think these scratches are on the AR coating or the crystal itself?
Are they fixable?
They on the coating, not the crystal. You can either have the crystal replaced, which would likely require a service along with that, or you can polish the coating off. I’ve done this with 1/2 micron diamond paste.