I have on occasion bought ducks that have come with lice, and many people don't seem to know what to look for, being shocked when I tell them their birds have lice. On Calls, I hit them right away with a spritz of Adams Flea & Tick spray under each "armpit", then follow up about a week later (after they have had plenty of time to bathe in quarantine) by giving them 3-4 drops of Ivomec by mouth. Remember, these are birds for pet/exhibition purposes only, so what you would do if you wanted to eat the eggs or meat, I couldn't recommend.
Some exhibitors make a habit of spraying their birds at shows, and this should not cause the casual observer alarm: they are often spraying to prevent from bringing any "unwanted guests" home on their birds and not because they have a lice problem...usually!