Hi Phillip,
Negotiate deals with organisations which allow a range of products to be sold...
I see it as simply a plural subject, ie '. . . deals . . . which allow . . .'. 
In addition, when I first glanced at the sentence I took 'which allow a range of products to be sold' to apply to 'organizations'.
I suggest something like
Negotiate, with organizations, deals which allow a range of products to be sold...
Best wishes, Clive