poke them with a needle and if oil leaks out you know they are using.
lol jk
most guys who use steroids look like shit, that is the honest truth.
they are so easy to get and affordable that it is hard to find anyone who has never used them before.
i would guess in the US if you go to a typical franchise gym more than half the guys you see have used or are using. and that is a conservative figure and includes pro hormone use. remember up until 3 years ago you could go on ebay or any site and buy pro hormones which count as steroids