I received USDT from an unknown source — should I send it back, and can returning it cause problems?
Don't rush to return it. Unknown inbound transfers usually fall into three kinds. ① Address-poisoning dust or zero-value transfers, meant to get you to copy the scammer's address from your history later — returning one means initiating contact with that address. ② The "sent it by mistake, please refund" scam, where someone contacts you and asks you to send to a different address or return more than you received. ③ Funds with a problematic upstream, where sending them back adds a two-way link between your address and that source. The safe course: check the sender's address against risk lists with a free lookup; ignore small poisoning transfers and never copy that address from your history; for a genuine, larger mistaken transfer, return it only to the original sending address — never to a new address the other party names — and keep a record of the exchange.
Telling which kind it is
Zero or a few cents, from an address whose start and end resemble one you use: poisoning — ignore it. Someone contacts you pushing for a refund, especially to a different address: treat it as a scam. A normal amount from an address that hits a list or shows one-hop taint at oceanalt.com/en/check: leave the funds untouched and, if needed, explain the situation to the exchange or platform you use.
Where to start: free address check · API docs · watch an address
Boundary of everything above: a screening "clear" only means no match in the data held, never a safety guarantee; this page is not legal or compliance advice.