We are having very similar situation like you said now. You can appeal to the county within 60 days from the date of
purchase (in MD) as a new owner. And almost assured, they will tax you based on some ridiculous #s if you don't appeal. From what we can see now (just submitted a few days ago), seems this is the way with a better chance to succeed.
MD's property tax website:
www.dat.state.md.us