Just for the record, I'm a hobby seller and only sell a couple times a year, so my selling experience is limited.
Hens sell great, I can sell them 15$+ apiece with no issues.
Chicks though don't go so well around here, since most people that want to buy are in city limits and can't risk roosters.
I just use Facebook. Look for "<County name> poultry swap" or "<city name> buy and sell".... groups like that. Watch out though, some groups do not allow animal sales and facebook is strict about it.
I hand deliver the chickens as I don't like people knowing my address, or do meetups at public places such as gas stations, it might be wise for you to do the same. Then you know they all got to their new home alive.
I usually only sell to people buying over 50$ worth of birds to keep it worth my time. Only getting a 20$ bill really doesn't pay for anything.
I do not refund birds, it is the buyer's responsibility the second money is transferred. I've never sold sick birds and never would. I'm honest with their laying abilities as well, especially if I'm selling older hens.
If I have a necropsy done, I make sure to post the most recent results on my advertisement so people are aware. Obviously do NOT sell if you have mites, lice, or anything at all wrong with your birds.
It may be wise to have a plan B just in case the chicks don't sell. Make sure you're able to comfortably house them.
I hope I helped you somehow! Sorry I'm not a professional, but I thought I'd share how I do things. If you have any more questions for me just ask ❤
Good luck!