If you buy from a reseller you will have both options should the need arise … you can claim your rights with the reseller, or you can claim Fairphone’s own warranty. Trader and vendor are different entities. Your choice.
If you buy from Fairphone, you still have both options, but you claim them with the same entity: Fairphone. No choice of a reseller which might be more nearby relative to your place, or speaks your non-major language (which Fairphone staff might not speak).
As to why they sell via resellers … For a start they reach more people this way. And they load-balance distribution (they don’t have to manage every sale themselves). And … probably there’s other stuff I can’t think of.
Resellers also take a bit of the enterpreneurial risk off Fairphone’s shoulders - FP3s sold to resellers are FP3s Fairphone won’t need to sit on anymore should demand be below expectation (which fortunately doesn’t seem to be the case right now). Easy revenue (even when the revenue per unit will be lower than from direct sales through Fairphone’s own shop). But maybe that’s just what you meant by “load-balance”.
I guess “load balance” meant, that FP is sharing the burden to distibute the phone.
They will save administrative costs.
In my opinion the main advantage of distibution via resellers is to be more visible on the market i.e. reoch more people as @AnotherElk correctly stated.
Those resellers have lots of customers and do their own advertising and marketing.
If they additionally share the values of Fairphone, like memolife, vireo and faircustomer, so much better for reaching the right ones.
And memolife.de (for private customers) as a surplus has a business-customer shop (memo.de) as well. And both shops present the FP3 on the landing page.
The lower amount of money they get for a single phone is outweighed by the higher number of sold phones.
Plus all the other reasons of course.
Buying with Fairphone still means more money in their pockets; though not in yours, as you might have to pay a few Euro more for shipping.
Selling by instance through a reseller which is a provider can give you the opportunity to buy the FP3 with a monthly subscription. So you don’t have to pay the full amount in one time.
This makes the FP3 for more people payable.