Gvilleguy is correct on the bullying issue. This can also occur if we just put any male and female together. With either species in this genus, the common or blue ram (Mikrogeophagus ramirezi) and all its artificial forms, or the Bolivian (M. altispinosus), the options are the same as the fish behaviour is the same.
If spawning is the desire, I would select a bonded pair from the dealer's tank. It is usually pretty easy to spot a pair that has bonded [I can explain further if asked]. The other option is to acquire a group, say 5-6, and allow them to pair off. The problem with this is having to then dispense with the other three or four. Depending upon the tank size (which you haven't given us) leaving them together is not always safe. I have had a Bolivian male kill a female even in a 5-foot 115g tank because they did not bond of their own accord.
Some sources say the bond is life-long, others disagree. But whichever, it still remains that the fish will be more likely to get along if they have selected each other.
Byron.