One of the most crucial: Always call!
In the age of email and texting this may seem old-fashioned, but I can't stress its importance enough.
Not all sellers check their messages obsessively as most of us likely do. I can't count the number of times that I've written a seller only to hear back from them days later because they haven't logged onto their mail. A good number of them also wait and mull the offer over before replying. In the mean time, others come pouring in and they can take their pick.
Calling forces the issue. Few will ignore a ringing telephone and once they've made that personal connection with the buyer, it's much more difficult for them to delay, waffle, or back out.
If the seller doesn't leave a phone number, just send them an email with yours and hope for the best.
I must say, I'm not really one for phoning up random strangers. It just kind of weirds me out, so I sometimes break the "always call" rule. Almost invariably, this leads to me getting burned.
Take today for example. I found a listing for two Overman pod chairs at $15 a pop.
Great deal! I arranged pickup after work but had the brilliant idea of getting a head start to avoid rush-hour. Craigslist shows the general location, so all I needed was a reply with the exact street address and I was set. Surely they'd respond as quickly as they had to my first few messages, right?
You already know how things turned out. Don't ever make this rookie mistake! Get on that phone!