I get rid of a lot of stuff on Freecycle, and I do a lot of this legwork in the intital ad. I try to get everything out of the way in advance. Something like this:
"I often get asked how I'll decide who will get the item I'm freecycling. The answer is that the first person to respond will have the opportunity to pick it up. If that person doesn't pick it up within 24 hours, I'll offer it to the next person. My goal in freecycling this is to get rid of it, not to store it, so please be willing and able to pick it up by Tueday, June 27th if you request it."
For Craigslist (which I only use for selling DVD's), I always add:
"I'll only be accepting cash as payment. Be prepared to pay you when you pick up. I've listed these as a lot because I don't want to have a lot of pick-up and payment issues. So, offers must be for the entire lot, I won't be breaking up the lot. Thaks!"
I have cut-n-paste replies for various scenarios and I respond to everyone. ("Thanks for checking, but I've already sold/given it away. I'm sorry and good luck finding what you need!") The only exception is for people who don't follow my instructions. I don't respond to those at all, because I don't want to deal with them.
("How much do you want for CSI Miami Season2?" = Delete.)
These are just some templates I have, and I adjust language according to the item, my needs at the time, etc.