Musical instruments aren’t cheap items and most of the top of the class ones can sometimes cost more than a brand new car. That’s why it is very important to ensure the authenticity of the instrument that you’re about to buy. Most of the top brands have their unique indications or signature. You just need to know them to make sure that you aren’t having the replicas.
Those genuine ones are being displayed in reputable stores like used band instruments from guitar center or similar establishments. Don’t be lured by cheap prices or too good to be true discounts because genuine items are most of the time expensive.