It's an iridiovirus, if you do a search for dwarf gourami virus you'll find much more than I can tell you.
From what I remember, just observe them well prior to purchase and make sure that they're mobile and inquisitive, you know, general good practice.
If I were after one I'd probably wait until they'd been in the store a week or two, maybe see if the store knows their provenance.
The honeys are a little less flashy, but the male has awesome breeding colors.