Speaking for myself, I personally check the areas I report on regarding navigation. It's not possible to check every single anchorage in a given season so I use a two year 'rotation', but Great Lakes anchorages (Georgian Bay, North Channel) tend not to change significantly, unlike anchorages in tidal areas, where shoaling, etc. can effect changes in short periods of time.
As for the marinas, those can often be dealt with using other sources for information when I can't personally visit them.
In the area I write on noted above, I make a point of checking the Active Captain posts - many of them are inaccurate or incorrect, and I've said this publicly before, so I'm not piling on here. The problem isn't Active Captain, but the way in which information is provided to AC, and other 'crowdsourcing' sites.
Transients (for example), who travel through once, get lucky and find the one 'sweet spot' in an otherwise marginal anchorage and report it as being a gem - or find the one bad spot in an otherwise great anchorage. Also - the Small Craft Route through the 30,000 Islands is very very tricky, with lots of granite and narrow channels, it's far beyond what the ICW for example presents. Boaters not experienced in reading these conditions will report inaccurately on the route, although tens of thousands of local boaters safely and confidently use it every season. I've been sailing and boating in the region for 40 years btw.
As for what checks Active Captain provides on its postings, I have no idea. And since the owner of AC has never been to the Canadian Great Lakes...
The rationale, as I've heard it explained before, is that the sheer volume of posts will provide a check on the information. I don't buy that, and I'm not real keen on reading 25 posts while trying to figure out just who knows what he's talking about and who doesn't.
I don't know Shellenburger, so I can't comment. I can say that I recently turned down an assignment to write on the CB because I felt I didn't know the area under discussion well enough to do a credible job.