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

Isn't all this terrible left wing money grab the OP is talking about happening in the Good Ole Boy state of Tennessee? What's California got to do with taxes this Red State is stealing from it's fine upstanding citizens? 

I’m not sure what Tennessee requires... but... I thought they defined a "seller" as a legal business entity who sells at retail to consumers, as the type of transaction upon which they levy a sales tax.

I am unaware that they levy any sales tax on a simple sale between two private parties, in which the seller is not such a "seller" as defined by the Tennessee "Sales and Use Tax Code." With the exception of when you register a vehicle or boat from such a sale.

Further, it appears that the maximum sales tax rate in Tennessee by all jurisdictions is 9.75%. To arrive at a "sales tax" bill of $665, would imply the "retail sales price" was $6820 - which does not appear to be the case here.

I’d wonder if the "tax bill" is actually a scam!

I’d contact the Tennessee Dept of Revenue... directly... via their published phone number and ask them. I doubt you’ll find they sent you a sales tax bill for such a transaction on an amp priced as low as you suggest, which was purchased from a private party (not a retail seller).

On the other hand... if... you actually did purchase from a "retail seller" as defined by the tax code... and... the real value of the amp is as you suggest (and not $6820), then you will find the actual "sales tax" is very likely less than $50 or $60.  

When the state cannot collect a sales tax from a seller in another country (or another state), it can impose a “use tax” upon the purchaser often at the same rate as the sales tax. And I believe this is true in a private transaction between a buyer and seller via Audiogon although that transaction and the resulting use tax is seldom ever found.  The buyer is theoretically supposed to report the transaction to the state - never happens.  It was pure (bad) luck that the tax collector found out about it.  It was probably an error in valuing the amp by a little bureaucrat in the Tennessee department of revenue, not a Qnon conspiracy of Democrats.  A lot of venting going on in these posts. Years ago I purchased an $8,000 pair of Focal speakers for $5,000 from a Canadian dealer. I may have paid customs on it, I don’t remember. But years later the California Board of Equalization caught up with me  - the purchase was traceable  - and I had to pay a Use Tax based upon the $5,000 purchase price, plus interest and penalties. No Big Brother paranoia was involved here.

You don’t pay sales tax in TN on a used item.   The state made a mistake and must think the amp was new from a dealer.  
Parts Connextion is an audio parts seller located in Canada and changes no sales tax on orders to the US. Do they have to? Don’t think so as they do not have any physical or other connection to the US (nexus)  I am aware of. 

When I bought an amp from Parts Express, I got the wrong model so it had to be sent back and I had another one sent to me. When returning it, I was told to state it was going back for repairs or a mod to avoid any hassle with customs and the whole declarations mess, and that was many years ago.

Things haven't seemed to have changed so I wonder why the OP wasn't informed about it or it could just be some overzealous official in TN.

All the best,
Nonoise