there should be a trade button on their profile but only if they have a rare to trade

"SEND TRADE" is what the button says and not only your trade partner needs to have at least rare items but you too need some items before you could send trade requests to the player you're trading with.

Hello!

Head over to the users profile and select the "TRADE" button, if it's not there they either have no rares or you dont have rares.

Thanks, Deadly!