As far as I know when a transaction is double spent, the first to be included in a block and start receiving confirmations is the going that is going to pass and the other one will be forgotten later on.
Any way, whoever sent you these coins is not trustworthy. He made this double-spent transaction to make you think you received the money. In fact he put lower fees on yours hoping that it won't get confirmed before his.
It doesn't necessarily mean that person is not trustworthy just because he used double spent - depends if the double spend was to the same address (1st and 2nd time). As in past and now when I send transaction with minimal fee and I wait like 2days or 1 day I usually double spend it with a higher fee to the same address so that I don't want eternity for my transaction to be confirmed.