I did a little experiment last week and displayed a couple beats as "SOLD" to push up demand. The general mindset is if customers go to your beat store and see that people are buying and seeing the "sold" badge, they will try to lock in any existing beats in your catalog.
Is it underhanded? Maybe slightly especially if you "unmark sold" it and causes a little confusion.
That being said, the results were positive. I gained more interest in my product via email and in the make offer option.
Mark some beats towards the top as "sold" and get traffic to your website. I'm not saying you should do this but all for experimenting, some of you may say it's unethical but to me unethical would be relisting sold beats after it's been purchased.
Big companies do this by releasing limited quantities or special editions to generate demand. When I go to a clothing website like "Supreme" for instance and see all the sold out products and makes me want in, this is just how the brain works.