In fairness, it seems like they did at least some basic testing because, well, they said so, and they'd also determined his wind attribute (something long speculated on but only now confirmed). The only thing they didn't test was his healing magic, and the excuse is definitely glasses dude just not wanting to because "He's Volundio, fuck that", but it's not an entirely unreasonable one.
I think the point is, that casual judgemental observers can't easily decipher that, and thus are discriminating jerks against those with similar looking scars.