Who is responsible for a previous owner's outstanding ad-valorem taxes?

Hello,

I bought a used car for cash, when I got to the DMV and tried to get the tags, I was told that there are outstanding taxes that the previous owner incurred for not renewing their tags on time. The previous owner’s birthday was in 2/09, the car was repossessed in 5/09, I bought the car in 7/09. I called the dealer back…basically they are not responsible to pay this and hang up on me. I don’t understand how I’m responsible for something that was incurred prior to me owning the vehicle. Is this legal??