i've sold a lot of stuff on cl and i follow a couple simple rules:
1. cash and local only
2. i tell whoever says "I'm interested" how many others may be interested and I use the order they contacted me and tell all where they are and if they want to be contacted if it doesn't sell before their place
3. if someone says that he'/she'll show and doesn't, they don't want it (whenever this has happened, they've contacted me immediately with the reason).
I've had people agree online or by phone on a price and then try lower when they come to pick it up. If we've agreed on a price, I go with that. If they don't want it at the price we agreed, I don't sell it to them....they've made the trip to me so it's no loss for me.
The only time i lowered a price on something was a cellphone...we met in a public place and I saw he was home from Iraq (he was a marine....I gave it to him and thanked him for his service.