This is your shotgun:
Below is a Grade 4:
Below is a Grade 3:
Below is a Grade 2:
IMO, your shotgun looks to be a Grade 3, with no finish left on the receiver.
Any gun is only worth what someone will pay for it, and collectors like "condition", meaning high remaining percentagee of original finish.
A rough estimate of your shotgun's value can be obtained via googling "Ithaca Grade 3", then checking for a sold gun in like gauge (you didn't mention what the gauge of your shotgun is) and condition.
BTW - As a rule, the smaller the gauge, the higher the value.
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