The scammer advertise on Facebook, claiming that they have huge number of Martin Guitar (very expensive guitar) that stuck in Custom because of not meeting export rules. They claim they are now working with Custom to sell it at only 10% of original price. They accept cash on delivery, so no payment upfront.

I checked with Custom and Custom said this is not true, there is no such thing.
Most likely they are selling fake guitar or just want to collect your details.