It depends on why you have fish. some people just want something colorful to look at (e.i. flowerhorns). others want to to have predatory fish (cichlas, wolf fish, piranhas........). you also have the ones who want the rare fish whether they are colorful or not( ramsdeni has no color but i bet if someone had a pair for sale they could get a nice chunk of change for it). then you have the ones that just want to help conserve and spread out cichlid species who are diminishing in their natural habitats.
either way we all love fish