As Kellysayers has said, what are they going to do? Demand to see receipts? I travel over to New York every year and buy clothes which are similar to the ones I wear anyway. We're talking about the reality of the situation but you seem to wish to have some kind of lofty discussion about "silly excuses". If you've a jumper folded in your suitcase with no tags on it how does the discussion go with the Customs official? Your comparison with TV licences is ridiculous as there are technical issues there. "Where and when did you get this jumper?" "In Arnotts a couple of months ago""Can you prove this?" "Not really, and I'm not being funny but could you?""OK, move along"On the other hand if someone starts splutering and blushing and saying "Mmmm, ehhhh" then I'm sure they get hit.
OK then, you win. These professional Customs officers (who on a bad day will be dealing with drug dealers and professional cigarette smugglers) are going to get all flummoxed and intimidated when the shopper asks them to prove their position. Apologies for my obvious error.
I guess the Customs guys are far too dumb to have worked out that Abercrombie & Fitch isn't sold in Ireland at all (given that any shopper who has a teenage in their extended family is likely to have have their case full of A&F overpriced tat).