Thanks, Wekkel! You say it correct.
If people buy with BTC the tokens become visible in their Wallet on NEXT.exchange.
If people buy with ETH it will become visible in their Ethereum wallet.
In this case, he created an unique BTC address on the NEXT.exchange page, where he transfer BTC and for exchange he got 400 NEXT tokens. The tokens are visible on his member page. Instead of looking there, he is going into panic mode and call us scammers?! Thanks, you also a happy new year.