I can not agree more with you on the idea 'follow the way natives speak'. However, sometimes I get confused by the grammaticality. Hopefully I can get some clarification from you.

1. Sometimes people say 'it ain't a smart chocie....' or 'He ain't....' Why 'ain't' is used? What does it actually stand for? 'aren't'?

2. I always hear my co-workers say: there is two things we need to pay attention or there is two people who.... why 'is' is used instead of 'are'?
I understand that when we are talking about 'things as a whole', we may take it a a singular. However, I don't think the above two cases fall into this category easily. Is it informal English? Do people actually write in this way?

BTW, the people I am talking about are well-educated native speakers.