We got this pair of Bolivian Rams a year ago from an individual. They are really nice specimens and we assumed they were a pair. After our successful Discus breeding, we moved them into the breeding tank hoping for similar success. But what we saw was fighting, and when researching how to sex them we found it is nearly impossible to reliably determine it from appearance alone. We did also discover that it's not uncommon for a pair to fight, even after they have free swimming fry to protect!
To increase the odds of having a female we bought two more at a local store after spending a significant amount of time trying to find ones in the tank that looked different from the rest. Since temperature and breeding conditions can affect the percentage of male and females in a brood, it's possible a fish store could have all males. But we gave it a try and kept this pair in a quarantine tank for a while before adding them to the big tank. It turns out that apparently we ended up with a pair as several weeks later we have fry!