I bought a used car and transferred the registration from my older car. I questioned why the reregistration was $37.50 higher than my old. Dealer wrote wrong weight. How do I get it fixed and $ back?

The vin should have given you the right info, but what you have to do now is to either go to AAA IF you are a member or back to the DMV with the proper information and change it

You would have to get the dealer to rewrite the bill of sale indicating the vehicle weight and re-submit the registration application. You may want to fill out this contact form with the vehicle registration information to learn whether a DMV supervisor can complete that change for you: http://www.dmv.ri.gov/feedback/