I use bleach water for sanitizing. It's inexpensive and it works well. Wear gloves to prevent skin irritation. Some folks swear by Oxine. I've never used it, but those who do report good results. Oxine has a wide range of uses and benefits. It's worth reading about...
if you have time. If you have problems with lice on birds in the future, consider bathing each bird with Adams flea and tick shampoo. The next day, you can use 1/2cc Ivermectin pour on for lactating cattle. Get a wash basin from Wal-Mart (under $2.00) and add some wood shavings or sand to make a bathing box. Playground sand is a favorite bathing material, and it's inexpensive, but it needs to be in an area where your barn cats can't get to it. You can sprinkle DE or poultry dust in the bathing box a couple times each month.
You're the buyer, so you're entitled to check for creepy crawlers. Check around the vent, under the wings, and along the back of the neck. Then go back and check around the vent one more time.
If I think a chick is male, and I only need females, I take one that I know is male in one hand and the bird I'm considering in the other, and then I hold them close together to compare combs and wattles. You're the buyer. You don't need to apologize for being thorough. Take some hand sanitizer with you and use it before and after holding birds. You want to discourage unwanted passengers (both seen and unseen).
A lot of people will have chicks and juvenile birds at P.O.O.P.S. It means waiting until June 14th, but in the mean time you could construct some awesome chicken pens : )