It should be بلدُكَ with dhammah on the daal
Should be baladuk(a). This mistake is common among Arabs and is repeatedly made in this course. It's quite tiresome.
Mistakes can't be common among Arabs when it comes to Arabic. How Arabs commonly speak Arabic is what determines what correct Arabic is.
Incorrect. Native speakers of any language regularly make grammatical errors. Plus, this course is supposed to be for MSA, for which it could be argued there are no native speakers, so your comment isn’t really applicable.