just my tongue-in-cheek opinion here:

the easiest way to tell if a drinker is an alcoholic, is for them to see if they can stop drinking without any outside assistance/support.

i'm not suggesting that they should stop forever (if it turns out that they are not an alcoholic). just for a short while so they can see if they can do it. i dunno, maybe like a year or two, maybe 3 or 4?

if they can't stop, obviously they are an alcoholic

if they can stop, perhaps they may not wish to go back after all…