I have had a bolivian for 4 years now and he is one of my all time favorite fish. His mate died of a tumor about two years ago and since then he has been less aggressive and much more fun to interact with. The first time the pair tried to breed though they attacked my then 12" long common pleco and alternated attacking his head and tail until he got fed up and buried their nesting site with a layer of gravel.
As for purchasing, when looking at a tank full of ANY kind of cichlid at a petstore I try to identify a pair in the tank myself instead of asking an employee to sex two at random (but maybe I'm just that way
) Look for two displaying to each other or defending a small territory in the store tank (a lot of pairs will take up residence in the corners of bare tanks). This IME has been the best way to get a compatible pair that will breed later on (the hard part is just keeping your eye on both of them as they're being netted).