Well just like you don't know whether one is dumb or a potiential PWS before he starts to talk to you. I've run into at least six PWS in total hitherto cuz some of them had announced they are PWS, and the others were manifested to me cuz their stuttering symptoms were very obvious and alien. If counting me, my father and my father's brother in, then 9 PWS I've met in total so far. But stutter is occasional and changable. So maybe someone who just had a short talk with you is also a PWS although he or she is not a severe PWS or they just 'changed' words to avoid stutter like some PWS are doing on this sub or else.