Do I need to pay Massachusetts state tax when I bought a camper in Maine and sold it in Maine never registered in Massachusetts

[DanielV01]

Probably not.  This falls under use tax.  The idea behind use tax is to make sure you are paying a correct amount of tax for articles you use in your state.  You might not have had to pay Massachusetts use tax on the camper anyways (because you paid Maine sales tax), or the use tax would have been reduced by the amount of sales tax you paid on the camper.  But you only pay that tax if you use the item in Massachusetts.  Since you did not use it in Massachusetts, you do not pay use tax in Massachusetts for the purchase.

Having said that, if you sold the camper for a gain, (it's likely you sold it for less than what you bought it, which would not be a taxable sale), Massachusetts does tax the capital gain.  However, you do not have to claim use tax on the camper.