I wouldnt blame the person working there at all, before i read the article i didnt even realise it was a man utd shirt and thought "YSB" was for Yossi bennayoun.
But yeh i know a few people who work in sports shops that do the printing that don't even watch football, as for knowing about it, until this year i didnt know about it.
If i was in the shop i would possibly question what the stuff meant and im sure he would have a valid believable story lined up to cover himself..
Fully blame the fan that asked for it printed.. terrible