agree with everything gigas12 said , a young micro should be bright in colour and allways active with no visable scale damage or holes in the scales , clear eyes and shop should be able to demonstrate that it is feeding well , ask to see it feed and ask what they feed it on, a varied diet is best as if only on live may prove dificult to wean off . a lot easyier if allready accepting dead food from shop. all fins should be compleate any sign of fin damage suggests it has been bullied and may be a week fish or have been stressed , if there is a few in the tank useally the biggest is the fittest as it is getting more food at feeding time.
channa micro is just a shortend name real name channa micropeltes = small scalled snakehead . micro - small and peltes scales and are indeed red as juvie i.e there other commen name red or redline snakehead , the adult fish is mostly white under body and black upper but has a shean which can be anything from green to blue and looks nothing like the juvie fish . there are many micropeltes about so you can afford to be very picky.
do be warned though of there final size even in aquaria they can and do reach 2.5 to 3 foot ,so a tank of 2.5foot wide minimum will be needed to house one
cheers col