Yes, spelling and grammar problems in the blurb are not a good sign (says he, checking his blurbs for the thousandth time and probably still missing something
).
I will add that some blurb problems aren't always the author's fault. Amazon seems to get it right, but even after repeated requests to BookBaby (my distributor, who, I guess, has little control over what end resellers actually do), my blurb still shows incorrectly on many sites. Some show the three paragraphs as a single big blob of text (which doesn't look good), one even manages to corrupt the en-dashes. And some sites show the "<p>" "</p>" characters that Lightning Source (for my paper books) require to separate the paragraphs. This has meant that I've been sure to stay away from more adventurous things like dialogue in the blurb.