Abbreviations

I am so happy to find this group. Hubby, kids and I have just started playing scrabble again after a long time and are having a disagreement about abbreviations. The directions clearly state that they are not allowed. However, some abbreviations have been used so much in our language that they have become words in their own right - and are in the dictionary.

Examples: biz, ex, lib

So...allowed? or not allowed?

Thanks,