What is the value of an Ithaca side by side double barrel 12 gauge shotgun with the serial number 270367?

That would be the Flues Model, made in 1915. You neglect to give us any idea about condition, so we will have to assume it is the typical 75%-or-less condition most of these guns are found in today. Also, we will have to assume it is a Grade 1. If all that is accurate, it would sell for around $300. sales@countrygunsmith.net