Independent salesperson(ISA) has roughly 2.25 million in guaranteed sales @ 12% net profit. (Varies from 10-15% over 5+years)
(ISA's previous company is being shut down due to owner liquidating for personal reasons. The 2.25m in accounts are all long-term relationship driven.)

The ISA wants to buy into ownership of an existing company in the same industry with about 3m in annual revenue, company value estimated about 1.7 million.

Obviously the ISA doesn't have a "company" to make it a merger, but the situation is almost exactly that sans employees/equipment.
How would one calculate the value of the business the IS would bring the table in terms of applying that value to purchase a percentage of the existing company?

Kind of a unique situation... not sure how to approach figuring the value.

Are you trying to create your own enterprise value, or do you view it as more of a cost sharing arrangement where you benefit with an override on income or in some other ways?

If the latter, you could bring them on at a bump vs. what they have been for a couple of years, and then move to an equity like split based on revenue that actually moved with them vs. your companies share. This would get tricky if the earnings quality or workload between them and your current mix are different. Also, would there be opportunities that come up that are hard to determine who drove it (them vs. you vs. y'all?)...again that would muddy the water.

If the former, you probably want to avoid having them fold in their book at your multiple. You are just diluting yourself and would essentially be betting on them pulling you along, maybe multiple expansion by being bigger, or some kind of synergies being achieved. I don't have a clue what the haircut should be, but you are the one with the infrastructure and the one with a business. That is worth something.

Growth is exciting, but not always the right move. Good luck!

Let me get this straight. You are bringing in business that nets $270,000 per year and you're trying to merge that with another business that nets about $400,000 per year?

If you merged, then couldn't you value each at their respective % of the total? Will the new company have to deliver on your sales? What's that worth? Will they have to spend money to scale up for that? How much would it cost you to build the delivery mechanism on your sales? How much do you trust each other to maintain revenue and net profits for the next few years? Would you consider a "buy-in" period of years and/or use part of your sales for a buy in? There's really too many questions to answer this with what you've given.