I use a similar method to this with cell phones on craigslist that I do pretty well with.
I agree 100% on personal response. It will absolutely increase your conversion rates by building a little rapport. I use a macro with a 1st respond and a 2nd response.
In addition to the generic macro text, I leave a spot blank up top to do a little bs'ing. Always addressing them by name if given "Hey Jon how are you this morning"
I always try to skim their email too.. (not read) but most of them have a reason for wanting the item "I need to replace my phone because my friend ran over it with his pickup truck" So I'll add "Wow sorry about your luck with your last phone, with friends like that who needs enemies huh!!"
The macro response usually includes something like:
"Someone is supposedly on the way to come get it, but I haven't heard from them in awhile so I'm not sure what's going on. If she falls through on picking it up, you'll be the first person I contact fair enough?" Then I go on to drop hints about this website I found it on.. but that "I can't remember exactly where it was" and "I'll have to do some digging around to see if I can find it.. but no gaurantees.."
You'd be surprised how many people will email me back with can you "please find the website for me!!", or "wow I thought those websites were scams i'm glad it really works please find it"
Of course the person always shows up, and I'm always able to find the website.
Little things go a long way. Infact if you have ever actually contacted someone in an ad on craigslist, usually you don't get a response and rarely is it personal. For people who use CL to buy things all the time, a little courtesy really makes you stand out.