Good names sell for themselves. If your names are good, end users will come to you. BUT you will have to be patient, even be prepared to hold and renew your names for several years. But you will be in a much better position, because the end user needs your domain, more than you need to sell.
If you "must" contact an end user, the name your are offering to them must be significantly better than what they are currently using. That sounds obvious, but I have seen domainers peddling atrocities. They make us look like fools and dreamers.
Well, i disagree. Not completely, because yes, very good names don't need any kind of marketing, but most of the time these good names attract domainers and investors more than end-users.
Sometimes a non-aggressive marketing campaign would be profitable. As told, few emails per day, not every day, to those companies or businesses with poor domain names or looooong one. It works especially for geo-targeted domain names imho.
Like, i don't know, think about [CITY]realty.com for example, where [CITY] is a big US city.
There are literally hundreds of real estate agency and businesses with poor domain like [CITY]realtybecauseyoulikeit.com or [CITY]etcetcetcrealty.com or [CITY]-realty-luxury-great.com.
They work, they have their own businesses running, sometimes they're having positive profits even with a very poor domain and a 90's styled website mostly because they have a solid offline reputation or something.
Often they tend to forget how important would be having a short and a direct domain, so even if your domain is a gem, they would never care about it.
If they are smart, mentioning the domain name in a short and direct email would be enough to convince them (if the price is reasonable).
If they aren't, well, nevermind.