What advantage if any is it to seller to have low item cost BUT inflated postage costs?
Purely adding a general reply to this question, rather than commenting on the specific scenario of the singlet and postage cost, since this may or may not be applicable to them...
Lower prices and a higher P&H cost can sometimes be for encouraging multiple purchases. (eg say a seller has a flat rate cost set up that's a bit above average P&H, when people know that postage is X amount no matter how much they buy, they tend to buy more to make the higher P&H worthwhile, thus 1 item at $2 won't really do anything much, but 20 items at $40 means the seller (probably) gets a more worthwhile sale, and the buyer may ultimately even pay less postage than what it costs the seller.
There's virtually no advantage to inflating P&H, except on the odd instance someone has a change of mind and wants to return - item price, but not postage, is refunded in those cases (generally, and also if facilitated via an eBay request). Not really a worthwhile tactic these days, all things considered (aside from bad impressions and people being tempted to take other actions to avoid losing such a large proprtion of the total payment, sellers are now able to implement restocking fees if they want to).
