DISCLAIMER, I am one of those people that Harry likes to talk about all the time (as in I constantly mix up its and it's).
It is (see what I did there
) okay, does not bother me one bit.
Forum posts are extremely informal English and by far most people do not even do a single pass proofread over them. Forums are closer to common speech than English class writing.
That aside, when SELLING my work - that is a different ball game. I know my weaknesses and have two editors fix them.
Mistakes still make it through, but that is true of all books.
As much as people claim otherwise, blurbs sell books. The normal shopper notices your cover and title first, your blurb second, the sample third. The amount of care an author puts into those things directly drive their bottom line. So if the blurb is bad, that is an indication of the amount of time they spent on the book itself. Pretty much the only time I would buy a book with a bad blurb is on a recommendation from someone whom I trust.
There are always exceptions, but in general if the blurb is bad, so follows the book. So I guess in a way that makes it a good thing, but I prefer not think a person doing poorly as a good thing, so I will hold to it is a bad thing - and a sign that the author needs help to really shine.