Yes and No. No, if one bought three Neiman Marcus shirts from such a source.

Yes, if one has bought many shirts, bags, laptops from these people; even in this case, prosecutors don't go after the fencers(middlemen) directly. They bust the small guys, who flip for plea deals. Then these 'thieves' wear the wire and sell stuff to these fencers; this is how prosecutors collect solid evidence to convict fencers.

Yes there is a legal responsibility for the buyer to use some common sense to think about whether items are being supplied to them legally.