Number 1 logical rule: You must be offering to them domains better than what they own.
If they own abccompanyinc.com, you can offer to sell abccompany.com; but not viceversa.
Also they may own abc.com also, and you may not know this, and not understand why they are not interested in your better domain.
This is obvious. But still far from being enough. In my experience contacting a potential buyer never works.
It may work indirectly. You may catch their attention, and they do research, and decide to buy months later, but not by replying the email. Maybe that email never reaches the ceo, and a middleguy will convince the ceo to get the domain for 100k, but offer 1k to you, and you will accept that 1k because of deseparation; or not knowing who the buyer is. And because of such a big price gap, your domain may never sell, because the ceo doesn't want to pay 100k. Just a possible scenario.
It is a mistake to assume that a hand regged domain can't sell for 4 figures or more quickly.
I'd handregged a .biz domain and sold it for 4 figures after 2 months, and its new owner sold it for 5 figures after 2 more months. Probably .biz was more popular at that time than it is now, but this is not the point. This can happen with any extension which is not very unpopular.
Also I registered keyword .biz domain for 5 usd, and sold it for almost 50k after 10 years, because that keyword became popular.
On the other hand I have top quality .biz and .infos I own since landrushes, and which never receive any offers.
If you offer a domain at a high-reasonable price, you look like a scammer. If you ask a low price you look cheap together with your domain (permanently). People don't like people who do favor to them.
I can imagine indirect methods, but I don't have tools; or they would be too time consuming.
People need to be exposed to some information from different angles to be convinced.
If only the seller is providing such info, this is unlikely to be helpful.
I don't like that domain business is very unpredictable. You can never know if you can sell your domain in 1 day or 10 years at 10 percent of its fair value. Only exception seems to be 3 letter .com's and similar domains. But even in this case you can't guarantee profit. One way to make things predictable could be using parking, but ppc services have a monopoly and don't pay little guys anymore. They use traffic to track people, not to convert them into sales directly. I'm not sure about this, but this is the impression I get.
In 90s you could make easy profit from .com's. in 2000s from google ranking+adsense, in 2010s from cryptos. Maybe I miss something.