I've also had moderate success at selling this way. About 50% of my sales have been the result of soliciting end-users through email. Most that I have sold this way so far have been mid $xxx and one has been mid-high $xxxx.
I buy mostly generic domains in .com and it's been rather easy for me to get interest and replies back from companies, but definitely, the hard part is trying to convince them of their need for the name.
It's true that most companies still don't get it when it comes to owning and using their industry or keyword domains, but because of this, you unfortunately have to be the "telephone salesman" and take the time to explain, even in email. In my experience of what has worked, anyway.
In just about every email I send out, I go a little into the advantages of "direct-navigation" and how it could help increase their company's revenue. I do this even if the domain I am trying to sell hardly has any traffic at all, because most of the domains I try to sell this way are products, services, etc, that are relatively new to the market and really don't have any yet anyway.
In these instances, what you are trying to sell is the "probability" that the domain in question will perform once the general public becomes aware of the product (or whatever it is) "because" of direct-navigation, if that makes any sense.
I also give examples of other companies, (sometimes direct competitors to the company I'm writing) and how they are using generic keyword domains in their marketing strategies.
It is a pretty "hit and miss" way of doing things like others have said, and it definitely takes a lot of emails and a lot of research, but I think that overall, it significantly increases your chances of selling as opposed to just waiting for offers.