the /pay -1000 thing would be a balance scam. And Lotteries are kinda like a Mystery Box scam. As for auctions, I have a tip: Don't buy anything enchanted. He may say its Silk Touch But its probably not.
Well, you can check what enchants are on the shovel in a shopchest. They used /iteminfo to check the Shovel's enchanted ID so if you just type in /iteminfo <TheID> it would tell which enchants it is. Knowing it's legit or not.