Received a Bill for State Tax on An Amp Bought in Canada Last Year

Just an FYI, I ordered a new amp from Canada in 2019 and had to pay customs, but not a state sales tax. CT

IMHO California is easily the US' most beautiful state. 

You may not like it, but many states have a sales tax and all states that have a state and local sales tax also have an accompanying compensating use tax.  Generally the sales tax and compensating use tax also applies to the sale of used merchandise.  If you are a seller located within a state, you are required to register as a sales tax vendor with the state's department of revenue and collect the tax from your customer on each sale of taxable merchandise and remit it to the state periodically.  If you are located out of state, in the old days the states could not force you as a seller to register and collect the tax for them because the states could not enforce their law in another state.  That's where the "compensating use" tax part of the tax comes into play.  Customers were required by law to remit the tax to the state on their own.  Of course most of the time people didn't even know the law, and even if they did, most did not remit the tax, and the states had no way to enforce the law.  Then, catalog sales took off and later the internet joined in.  Now states are able to get third party sellers like amazon to collect and remit tax for them and many states have formal relations with out of state mail order companies who often have brick and mortar corporate affiliate stores instate.  I believe the Canadians and some of the states have reciprocal agreements with each other.  So they report taxable sales to each other.  So.... you received a bill.  And you may have received a bill for tax on the sale, and then, when a repair was made, that too is subject to tax.  People may disagree about the level of state and local budgets, and reasonable people can disagree.  But taxation should be fair and equitable.  If a local merchant in a brick and mortar store is required to collect sales tax on new and used merchandise and services, why shouldn't a mail order catalog or internet seller be required to do the same? Not doing so creates a perverse incentive for people to make purchase in other states to avoid tax.

betting IL, CA, NY, NJ, MI, MN, WI, ….. LOL,
  Guy thinks like me  

Talk about dense.