Yes, it is mathematically ensured that the coin issuer cannot link the actual coin to the account you are buying it with. No blind trust needed, check the math yourself: https://en.m.wikipedia.org/wiki/Blind_signature For the specific implementation, you can check the taler source code.

Is is possible to trace back a gift card to the store that sold it? Maybe even the date and time? Then get the surveillance tape... If you pay with the same gift card more than once, all those transactions can be linked.