So it sounds like he hasn't paid you, which you didn't say explicitly, you said "no communication."
If that's the case, then I think you can take him to court, but as others have said, check with a lawyer. Someone above asked if his shop is open; there is the possibility that he's having cash-flow problems due to the virus but he should communicate with you on that, if it is the case. It doesn't in any way excuse his keeping your money.
As for a minimum, having worked in instrument sales I do know that often people have an inflated idea of what their used instruments should be worth, based on their original purchase price. I'm not saying that's what happened here, but a high-end, boutiquey type instrument will usually have very narrow appeal and so it's a good idea to specify what you will accept. A consignment seller has the option of holding onto the instrument forever, returning it to you, or lowering the price if it isn't priced correctly to begin with. But it sounds like you weren't dissatisfied with that part of it.
If that's the case, then I think you can take him to court, but as others have said, check with a lawyer. Someone above asked if his shop is open; there is the possibility that he's having cash-flow problems due to the virus but he should communicate with you on that, if it is the case. It doesn't in any way excuse his keeping your money.
As for a minimum, having worked in instrument sales I do know that often people have an inflated idea of what their used instruments should be worth, based on their original purchase price. I'm not saying that's what happened here, but a high-end, boutiquey type instrument will usually have very narrow appeal and so it's a good idea to specify what you will accept. A consignment seller has the option of holding onto the instrument forever, returning it to you, or lowering the price if it isn't priced correctly to begin with. But it sounds like you weren't dissatisfied with that part of it.