A few tips but aren't the only ones:
It's helpful to look for pins that aren't just stock/pinpics pictures, listings that have the actual pin's picture is an easier way to make a decision on it's authenticity quality.
Compare to the pinpics ID, look for any discoloration like "the eyes should be blue but instead are pink" etc sometimes color errors do happen though on official pins so it's sometimes hard to tell. If you privately ask the seller to send you a picture of the back and they refuse, "sometimes" that's a red flag, but not always.
If you see the same seller selling the same pin over and over when it should be an LE of 100 but clearly sold 200 for example. Definite red flag. However, if you see a seller with like 10 of the same pin of an LE of 50 though it might just be that they were lucky enough to get 10 of the 50! Just make sure to ask for pictures of the front/back just to be on the safe side.
Look at recent sales and try to determine if it's a "too good to be true" sale where it's far cheaper than it should be. A Jessica Jumbo Alice for example that's selling for $50 when normally it runs from 150-200+ is definitely a concern. Sometimes you can get lucky though! So while these tips are not a definite "it's fake/scrapper" guide, it still helps you be somewhat alert