IMO, if you are regularly in contact with a business contact, you can use email instead of PM.
There are, of course, other means of contact including Skype or social media. But I intentionally created a scenario in which I wanted the forum's PM system to be the only thing I wished to use.
Well I guess if you are creating scenarios in which you must give merit to yourself (and ignoring alternatives), this thread is moot.
Using some kind of key authentication, such as GPG, or using bitcoin signed messages would be superior to using forum PMs in pretty much every scenario.
Actually, there are no rules when it comes to meriting at all.
There's an official rule, visible when a Merit sources Merits a post:
It is not allowed for merit sources to sell their merit.
I don't think what the OP is describing would be considering selling merit.