Look for the most dominant and healthy fish. Biggest in a handful of juveniles usually means the most dominant and healthy. Gold Severum juveniles are very plain coloured, usually white, but Greens will show most colour and you can gauge reasonably well what the adult will look like.
Sexing, well some people will say that darker worm patterns on their face means it's a male, but it isn't always the case. Dorsal fin and anal fin extensions on Males are usually excessively large but won't become prominent until around 6-7" when the Severum really take their proper body shape.
Basically I'd go in looking for all of the standard things you look for when buying a fish, well looked after store, no visible disease in any fish, and what I've previously mentioned regarding size etc. Green Severums are a fish that really pay to shop around for, the variance in what these fish look like is huge. I've got one of the Paler with shades of yellow green with almost fluro face markings, as well as my larger Severum whos one of the straight up plain greens, but is usually a very dark olive with a solid mix of cream and red around the stomach.
No nice photos of my small guy, but here's my 5 1/2" Severum. Not 100% sure if it's male or female.
My advice is definitely shop around for healthy and stunning little juveniles. Both of my Green Severum were planned buys that were bought on impulse (shopped around until I found 2 that I was after).
