How would you tag something like this: https://www.recordnations.com/wv/goin’-postal-25401/
As either a shop or an office, depending on whether it gets a significant amount of passing trade. Assuming it doesn’t then I’d go with “office=” and search taginfo for whatever’s most appropriate - https://taginfo.openstreetmap.org/keys/office#values .
If you can’t find anything there then just use “office=company”.