Dwolla?  Really?  Dwolla?  An unknown internet site that takes forever and a century to clear funds, isn't a regulated or recognized financial institution?  People will accept a personal check LONG before they buy off a "now, I'm going to enter a few numbers into this web site and you'll see your money in your bank account in about 3 days.  Oh, and I'll need your account's electronic transfer code, and I'll be driving off with your car as soon as you sign that title..."

I too have bought several cars with cash, and I know what I'm talking about.  You clearly do not.  (p.s, other guy: instead of cash, try cashier's check.  most people are willing to accept that if you negotiate it beforehand).