Some scammers use scripts to lag the game during a trade, making it impossible for you to click "Unaccept" before they remove their pets.
Some developers use obfuscation (making code unreadable) or "anti-copy" scripts. However, these are often considered "security through obscurity" and can sometimes be bypassed by determined exploiters. For Players: Preventing Pet Theft Pet Simulator X - Anti Steal Download
If you are building a PSX-style game and want to prevent others from downloading or "stealing" your work, keep in mind that anything on the client side can technically be accessed by exploiters. Some scammers use scripts to lag the game