I had someone from a rather large company email me, all super interested, get them started on a trial then they'll pay like tomorrow. They just need to get started ASAP!!!!!!ones!!!! That turned into needing to talk to some business guy, who absolutely needed to talk to me on the phone, so he could ask me for our address and a phone number, which I emailed to him.
I deal with this sort of thing probably once a month. The larger and older a company it is, the more likely I'm going to need to jump through some hoops, rather than have them use our nicely automated purchase process. Filling our vendor forms, agreeing to their anti-bribery policy, giving them a "direct" email rather than support@, agreeing to net-60 rather than net-30 or pre-payment of service.
Is it awesome, no. But I do it. Joel Spolsky's customer service tip #6 (http://www.joelonsoftware.com/articles/customerservice.html) comes in handy. Pretend you've got a puppet, and you just need to make the puppet say something that will make the customer happy. It's not you, it's the puppet.
Because I've managed enough of these situations, we've built up a sufficient pool of customers that we have enough money to hire (part-time) someone more comfortable dealing with these tricky customers. Now I deal with them less, and more of them sign up. It's a fantastic circle really :).