Currency in Mostar

No, they use their own local currency - the Bosnian convertible mark - so be prepared to pay in their local currency. Make sure you have small denominations (avoid large bills if you can). I think some shops take credit cards, but I can't recall...I would say they would probably rather get cash.

We found most places did not take credit cards and we got convertible marks from the ATM. We did not try to pay with Euros or Kuna.

I was there in July and Euros are widely accepted. Most places listed prices in euros and marks. If you are only in the country for a day or two, some might suggest to not even get any Bosnian Marks, as certain banks are reluctant to change any leftover money back to dollars or euros. I personally did not experience the difficulty in converting money back (I spent all mine), but several different people gave me a heads up about that. It is true that credit cards are not as common as other destinations.

The Bosnian convertable Mark has a fixed exchange rate to the Euro, BAM 1.95583 = €1.
Unlike most currencies, its exchange rate (to the Euro) does not change from day to day.
This strange number is because the Bosnian Mark was originally linked to the German Mark, at 1:1, and when the Euro started, the rate to the German Mark was fixed at €1 = DEM 1.95583.

Thank you all for sharing your experiences and information!