There can be no simple formula for the revenue to be shared between you and your marketing partner.
The value you could consider parting with in terms of revenue earned due to the efforts of the marketing partner could be based on
- Your estimate of what it would take if you were to set up the marketing team on your own to achieve the numbers given by the prospective marketing partner you are in discussions with
- The valuation of the company if you were to achieve those numbers
- Your operational expenses for you to achieve those numbers
- Another important aspect you should consider is to put a value to your IPR. In no case you should consider parting with value of your IPR.
- The value of the share of the marketing company should be the valuation less your IPR in proportion of their marketing expenses versus your operating expenses.
In simple terms, this value does work out to anywhere between 5% to 20% of the revenue, that too, X% for revenues up to say $A, Y% for an additional $B and so on.
Perhaps, another aspect to consider is a non-exclusive contract with the marketing partner or if an exclusive contract is mandated, then make it region or geography or client profile specific
Hope this helps.