Reading Taler's website (https://www.taler.net/) it is not clear to me whether customer and merchant must agree to use the same exchange in order to perform a transaction.
It seems to be implied by the key interactions of a Merchant: "Create a reserve based on an incoming wire transfer from a customer" and "Execute wire transfers to merchants in response to validated deposits".
If this is indeed the case, then there's an attractor towards centralization: both customers and merchants will be forced to sign up with the dominant exchange for maximum interoperability.
Either exchanges are given an incentive to federate with zero friction for users, or the Taler network will inevitably become a centralized monopoly.
I understood the website the same way you did: the merchant must use the same exchange as the customer. I hope we're wrong.
For the sake of anonymity though, it appears to me that using a new exchange would be easy as you would not require to log in with an email and a password, but rather with a kind of web-browser extension or something similar. Each merchant could then become its own exchange, and you would only see a few big exchanges whose role would just be to make everything simpler for the merchant, and that simplicity would come at the price of an increased fee. This is a bit like what PayPal or Stripe are doing today.
It seems to be implied by the key interactions of a Merchant: "Create a reserve based on an incoming wire transfer from a customer" and "Execute wire transfers to merchants in response to validated deposits".
If this is indeed the case, then there's an attractor towards centralization: both customers and merchants will be forced to sign up with the dominant exchange for maximum interoperability.
Either exchanges are given an incentive to federate with zero friction for users, or the Taler network will inevitably become a centralized monopoly.