Do native speakers hear the difference between -ing and -in'?

The whole reason *in'* exists in writing is because people often pronounce *ing* that way. It is eye dialect.

Yes, but they should be able to comprehend with ease. As for the difference, -ing is made with the root of the tongue whereas -in' with the tip.

“In” ends abruptly but “ing” has an after tone, almost ringing.

Very clear difference to native speaker.

The difference is the sound. "Ng" is a digraph representing a single sound, and when it's replaced by "n'", that simply means that the speaker is using a regular n sound there instead of the ng sound. It's a very easy difference to hear if I'm listening for it, but if I'm not I *might* miss it.

Yes. But native speakers also often pronounce ing as in.

I can definitely hear the difference, but it's one of those things that I tune out unless I'm specifically listening for it. A lot of people shorten ing to in', especially if they're talking fast. I know I swap around between the two without actively thinking about it. It depends on the word that comes after and how fast I'm talking.

Absolutely. They sound completely different to our ears. Puttin vs putting, makin vs making, bein vs being, tryin vs trying.. it is not just the final consonant sound that changes but the vowel is different also.

Heat the difference, yes. Care about the difference, no. It’s an accent/dialect thing. We might guess where you are from depending on your use of in’ vs ing, but we can understand either just as easily.

yes, but it can be difficult depending on the word. '-ing' has a high 'i' sound (like the 'ee' in 'bee'), while '-in'' has a lower 'i' sound, almost comparable to (and rarely written as) 'en'.

yes, definitely.  

Yes, there's an audible difference. While its seen as casual form in writing, no one will give you much of a hard time about -in' vs -ing in speech though. An example to use would be "keep" *Keepin'* sounds more like "keep in" than "keeping"

I also notice when people end "-ing" words with "-een" as well. Like "What are you do-een?"

\-ing is pronounced /ɪŋ/ \-in' is pronounced /ɪn/ Which probably means nothing for you, but you can google the difference between n and ŋ and hopefully that will help. In my own words, n is pronounced with the tip of your tongue pressed against the ridge of your gums just behind your teeth. ŋ is pronounced further back in the mouth, by pressing the sides of your tongue against the roof of your mouth.

*ing*'s G is silent, so this syllable is pronounced like *een* (like in *seen*) On the other hand, *in'* is pronounced the same as the word *in* So: *Running* is pronounced "run-een" *Runnin'* is pronounced "run-in"

Yes. Most of the time we ignore, it except when it matters. For example "fallin' leaves" sounds too much like "fallen leaves" so cases like that I make sure to say "falling leaves". It also says a little about tone of the speaker.