We've worked as software consultants for a customer for 4 years, the relationship is good at all levels, they run a cloud platform and we've helped build their mobile SDK and other products.
In the past their customers would go to different providers to develop their mobile apps, but since we've developed the SDK we're in a very good position to develop their apps, our team is rather small and we don't have a sales team, we're pretty much engineers in business.
Now we've entered talks to develop consumer apps for their customers, where they would make the sales process and we'll develop and manage the projects; I think the best for both companies would be to split the revenues of the projects, but I'm not sure a 50-50 ratio would be appropriate.
They are very good sellers, and this would help our company grow significantly; I'd like to make it fair for both companies, but I know they could be tough negotiators. Our operation costs are low compared to them, they know and I think they might argue, or base their negotiations on that, however I don't think that's relevant to the ratio as long as we deliver.
What would be a fair percentage for them? Considering the sale alone.
If you have a good relationship with them and you can trust them to tell you the truth about the price the customer is paying (or you have visibility into the deal) then you could go for a split of the net, ie profit after you and they have covered costs. If it is more arms-length and they are buying from you to sell on at whatever price they can achieve, then I would keep it simple and charge them a price that gives you a good solid profit which you are happy with.
Personally I don't like profit share because a) it's very easy to cheat if you're doing the selling and b) when things go wrong eg you overrun on the dev or they underprice the spec, things go sour fast.
You can transfer your team cost +management fee , operate profit centre