I question this. "Free trade" (or any other trade) is not based on groups going toe-to-toe over the merchandising of "identical products of their own making". Rather, trading hinges on Group A supplying the needs (real or created) of Group B, and visa versa.
IOW, it's not trading your length of rope for my length of rope; it's to trade your length of rope for my length of cloth, or my netting (made from your rope,perhaps?), or 1/2 dozen of my chickens, or whatever.
The question then becomes: What would Neanderthals have that the Cro-Mag. want? Esp. if, as one Freeper pointed out, the Neanderthals were highly territorial -- and contentedly so. Frankly, the only thing I can think of is human chattel, whether slaves/field hands/mates(wives).
...the cultural materials of late-Pleistocene and aboriginal peoples suggest that such social traditions originated at least as early as the period 40,000–20,000 years B.P.
Cultural materials (amber, sea shells, stone tools) often occur hundreds of kilometers from their points of origin indicating intergroup contacts over wide areas (Klein 1989, 376–8). No such evidence of social contact occurs before the late-Pleistocene...Bottom line: if trading with outsiders is too much for you, your days are numbered.