There are certain patterns in transactions that make it apparent alt accounts are sending coins/tokens to themselves. Usually they have to do with the spacing of the transactions, the address type, and transaction amounts.

For example, if a bunch of accounts are all sending tokens to the same exchange deposit address within 1-5 minutes of each other, this nearly certainly means one person is flipping through metamask addresses that are all in one wallet that belongs to them.

Also, accounts that send entire coin balances (BNB and ETH, mainly) back and forth to each other often are likely to be alts just adding gas to their wallets to make token transactions.

The speed and coordination of the transaction timings occur in a way that renders it highly unlikely these accounts are just selling their tokens / BNB to a 3rd party.

It is of course ideal to substantiate connection evidence with social media proofs, but there are problems that can arise from that as well (bounty hunters copying the details of other hunters, for instance). That's why every connection should be reviewed on a case-by-case basis, and presented in a manner so the majority of people who look into it can come to the same conclusion.