wheel - 8:54 pm on Feb 17, 2010 (gmt 0)
Just to clarify - I am talking about a conversion action which is a 'contact us' type request or a lead - not a purchase (which may be different).
Given what you've described, in a contact us situation, I'll tell you the single biggest factor in conversion. It's time until you call.
If you're working 'contact us' conversions, you should be set up to call these people in seconds. Not minutes. Not in half an hour. NOW. Get them while they're still at the computer, on your website. Drop everything and call them.
The increase in sales by decreasing the time to respond beats every other thing I can think of.