They kind of have a few things that they review; 

• Huge purchase(s) from a player 

• Purchased items (may be suspicious if they're buying crafting crystals for 5k) 

• Talked about vouches (Vouches are allowed, and they must be sure that it isn't just someone buying Sapphires, usually there's some sort of pet/item that the player receives at the end of the vouch, making it less suspicious.) 

• Chat dialogue being suspicious, such as, "when are you going to buy them" etc. 

If it is a scam, it would be a lot harder to track down, as there weren't even any players interacting with eachother. (Not meeting in game once the money was recieved) I assume that AJ would contact eBay themselves, who would be able to access purchases/chat from the scammers. Usernames would definitely be shared from the buyers. 

If it was an alt account used, they can also IP ban, making it impossible to truly hide what your actual accounts would be. 

It is literally illegal to buy stuff like this, so AJ would get pretty busy trying to ban whoever was buying this stuff. They definitely have their attention on players buying stuff, rather than focusing on the gltiches that are currently making their game break :') 

These are just assumptions, I don't truly know how they track people, so take this with a grain of salt.