Yes, I know the definition of money laundering. I just don't understand how purchasing gift cards on ebay helps you launder money.
Fake large ticket purchases that are set up for the purpose of laundering, and the same people likely place insanely high bids to ensure nobody else can enter a real bid.
Say, put a $1000 bid on a $500 gift card. Someone bids 502, that 1000 max bid is still valid and bumps the current bid to 503 or whatever... this may continue until some illogical fellow bids a max of 550 or so, and then everyone gives up since it's no longer worth it.
Original very high bidder "wins", no actual goods are ever changed hands, but the money is moved across accounts. Legal transaction, helps clean up the money's origins.
This is just an assumption of how it would work on eBay. I've actually never given it much thought, but in the modern age, it makes a lot of sense for the cases where the paid bid is far more than the value of the item.