I Have A Nice Maximianus Follis

Quite a nice looking coin. I'd call it a VF. Thanks for sharing.

I like the attitude to grading.
When it comes to buying or selling, it is the attached comments that have a big influence on the value, because "like" for the most part, is subjective.

I noticed the silvering myself
If you give it an overnight in acetone to remove any oils
You might give it a brief ten minute bath in vinegar
This will brighten the silver up a bit

Be advised
Vinegar is mildly acidic so don't leave it for very long and don't rub it
Light brushing with soft tooth brush after rinsing

It will look rather drab when dry
A dab of coin preservative will restore the color
If you haven't got any a smidgen of Vaseline works well

The coin is made of "Billon" which at this time period is essentially a bronze alloyed with a bit of silver
In earlier times the silver was anything between 20-50%
Your coin is more likely around 5-10%
Higher silver content coins are safer to bathe in solutions to remove the grime
But with silvering you must take care not to rub the silver ! It is quite thin an will come away with little effort
The theory in coin conservation is to try and dissolve the grime and save the patina beneath !
A gentle brushing with a soft tooth brush is usually okay
But watch it very closely