[Taler] Exchange Fee Structure (was: Taler Android UX)

[Torsten Grote]

On 2020-04-13 16:56, Christian Grothoff wrote:
>> I guess it would need a lot of malicious consumers to achieve that
>> and imagine that one could put other defenses against that in
>> place.
> Tricky, due to customer's anonymity you don't really have any good
> way to do accounting, and no good way to tell legitimate from
> illegitimate requests. And of course we cannot simply NOT answer
> requests either.

I don't know yet how refreshing exactly works, but could there be a
refresh counter for coins high enough to allow legitimate use, but low
enough to prevent abuse?

> Well, it's of course more difficult ;-). Merchants can specify that
> they are willing to pay certain "reasonable" wire fees. [...] But
> imagine an exchange charges 1 EUR for wire transfers. [...] Here, the
> merchant additionally specifies an amortization factor (a factor of
> 40 means that the 80 cents are to be amortized over 40 customers).
> Then, each customer would have to contribute 2 cents in wire fees.
> But possibly not exactly 2 cents, if there is room from the deposit
> fees...

Uff. Complicated indeed. Would be much easier without wire fees, but I
guess you have considered that and it would run contrary to some other
design goal.

So as a user withdrawing money, I would want to be careful with
exchanges charging high wire fees, because that *might* increase my fee
with a merchant I want to pay.

Maybe when showing the fees, we could hide wire fees and closing fees
for future years when the price only increases moderately with an option
to expand the full details.

But really, from a consumer and UX perspective, exchanges that charge
for more than withdrawal (and maybe refresh/change) operations introduce
so much complexity that I have a hard time imagining this being used in
practice, especially when you compare it with the simplicity these new
fintech apps offer. Worse: The additional complexity can be used to
screw users over by hiding high fees in there.

So I'd say the wallet should warn about all exchanges making use of the
fee complexity that Taler supports until there is evidence from
practical use that the complexity is actually needed.

>> Interesting. Should we maybe have little info buttons next to the
>> fee labels with these explanations?
> Yes. Little info buttons, but then likely jumping to walls of text
> with the explanations ;-(.

If you want to support the full complexity and require users to
understand it, I see no way around providing walls of text. But at least
they are hidden by default and need to be actively opened.

Kind Regards,
Torsten