Something worth mentioning is that a number (by NO means all) of these "errors" mentioned here aren't actually errors but, let's say, variant usages--for example, they may be less common but still reasonably well accepted, or they may be regarded as perfectly correct in some regions/countries but not in others. Many questions of punctuation, spelling, and pronunciation don't have single correct answers; rather, they have several variations considered acceptable in formal writing. British usage of commas, for example, differs from American practice. British English typically gives collective entities such as companies and teams plural verbs rather than singular ones, as American English typically does. There are numerous other examples.
This isn't to say that I think "their" is an acceptable substitute for "they're"--my entire working life has been based on eliminating things like that. But it's just as well to keep in mind that not all of these issues have hard-and-fast yes/no answers.
This isn't to say that I think "their" is an acceptable substitute for "they're"--my entire working life has been based on eliminating things like that. But it's just as well to keep in mind that not all of these issues have hard-and-fast yes/no answers.

