Notes,
I respect your decision to notify them and keep everything honest.

I've read that in the past some unscrupulous mail order companies would send more expensive items than people ordered, then try to charge them the difference, so a law was created to protect the consumer. If what I've heard is true, they can't charge you more or even ask for the more expensive product back. (if they could it would put the consumer in a perpetual limbo of never being able to sell the item for fear that the seller would want it back).

If they sent it in response to your payment, it's yours if you want it. You can, however, elect to ask for your money back and return it.

I suppose you could also sell it, buy the guitar you really want and pocket the difference. It would be more hassle than the transaction you wanted to make, but at least you would be "compensated" for the hassle. As a professional musician you probably know a number of people who would be interested in a boutique instrument.

All this is hearsay... you may want to research consumer law to make sure of the rights you have in Florida. But I feel pretty sure that the ball is in your court on how to move forward. By sending you the more expensive guitar, they implicitly agreed to take a hit in order to process your order. Your move.

Not a bad position to be in.. much better than if they had sent you a cheaper instrument by mistake (or on purpose)

https://www.dropbox.com/sh/ey71h8ep047758h/AAC12jNM0Hz9Q8zsh5iDeqNHa?dl=0