I purchased my car in New Jersey in 2007 while I was living in Virginia. I paid the New Jersey sales tax. I moved to Maryland last month due to job advancement and went to register my car. I was told that I had to pay Maryland tax rate to register my car because the tax rate in VA is lower than MD. I tried to explain that I purchased my car in NJ, where the tax rate is higher than MD, but to no avail. I ended up having to pay over $800 to register my car.

If I take my proof of New Jersey purchase back to the motor vehicle department, will I be able to get my money back, or at lease a reduced rate?

Did you not register and have tags on it from your other state.
There was no "sales" tax due at all since that was paid years ago,

You were merely transferring the title and registering a previous licensed vechile, the fee is about 180 dollars depending on size of vechile

MidNightMother:

Take the paperwork to the MD tag office. The worse thing that could happen is that they say No!

Chuck:

Many high-tax states have "retroactive" rules to prevent MD state residents from registering their cars in other states, wait for a period, then "transfer" the tags to Maryland without paying the higher Maryland state sales taxes. I suspect that is what happened here.