I do this at the store all the time!...lol....This is what I do...
1.Look at the fishes health and see how it supports it self.
2.Look at the 2 fish in the tanks.Look at which ones l like.
3.Ask staff about the fish I have looked at(testing their knowlege).
4.Then ask if the teo fish I like can be put in a tank for a bit to see if they fight!
5.Once they say yes(most will but never know!)
6.Wathch to see how staff handle the fish while be moved to new tank for a bit( I do this to see if they damage the fish,when fish are damaged they tend not to fight)
7.See how the fish react with each other.
8.Watch for about 10 to 15 min( can take awhile to see what happens)
9.Look at they way the fish swim and see if they flash at ecah other if so thats really good!
10.If they get along make good offer for pair and they exept say SOLD with a passion!
Thanks,
Austin/clowns101