I don't think an above board negotiation to purchase in bulk is correct to refer to as collusion. In lieu of other details it's just a purchase agreement.

Collude is originally a combination of Latin words, isn't it? "co"/"com" which means with, or togther, plus "lude" or "ludere", like means something like "to fight" or "to play" I believe. But - I'm not a native speaker so maybe I should have used another term.

"Collude" carries a strong negative connotation, possibly but not necessarily criminal; certainly within a grey area though and at least somewhat secretive. For above board dealings in the open perhaps "cooperate". If it took opponents by surprise and left them disadvantaged then perhaps "outmaneuvered". If it was open and legal it could nonetheless still be "objectionable" or "callous".