Working in the trade, i see a LOT of Dwarf Gouramis and these have gone from being one of my favourite species to one of my least favourite due to the stress and hassle and death!
All gouramis i get come in from reputable suppliers and are in good health but the stress of the shipment i dare say doesnt help but whether it is a day or a month, you generally always see problems in all the colours.
Frankly, im sick of the species, if it isnt one thing it is another, bacterial and fungal infections often around the mouth and pectoral fins, sunken eyes and bloatedness of iridovirus...
I have fallen in love with Honey Gouramis and Thick Lipped Gouramis, You can get Thick Lips in the same colours as the Dwarf Gouramis and they get to the same size but have none of the same health problems. Personally i prefer the golden honey gouramis, i have a group of them and they are cute as anything! They are more active than the dwarves and less finnicky!
If i was going to sell a dwarf gourami to anyone, i wouldnt sell them to anyone with a tank under 6-8 months mature and with good filtration, id even be tempted to ask if they minded me doing a water test to check... thats how little faith i have in the general health of dwarf gouramis...