If you plan to make money as a guest post publisher, I think you need to have a solid plan if you want to make real money.
Now, if you wanted to just make beer money of side cash, publishing guest posts on a low-level month after month will probably do the trick.
Of course, this depends on how well your site ranks and if it has solid SEO fundamentals within an identifiable niche.
The downside to making money full-time publishing guest posts boils down to volume.
As you probably already know, not all niches are created equal.
Some niches get a lot of guest posts activity and people with matching bids.
Other niches are very stagnant.
You may get a proposal every once in a while, but these are not enough to earn a full-time living.
How do you fix this problem?
Well, if you're serious about choosing guest post publishing as a profession, I suggest that you build a network of blogs in different niches.
This way, once you build solid link equity for your network, you can get a steady stream of customers.
This is true for "real websites" as well as "built-for-links" aka PBN networks.
As you can tell, when you go into the link-building section of this forum, there's a tremendous demand for PBNs and niche-specific link sources.
But those websites are not created equal.
Some are built from the ground up purely for guest posting.
There's nothing wrong with that, but you have to know what you're doing.
On the other hand, if you come up with a truly organic site with real traffic and a fast-growing brand, you probably would make more money down the road if you know what to do.
Because at the end of the day, a backlink coming from such a "real site" is going to be worth more than a link from a website based on an expired domain that has solid backlink equity.