Hard Brick I747: yes, there are options
The definition of "Hard Brick" is a phone that cannot be booted into any mode (including download, recovery). Worse case is a phone that does not respond to the buttons at all (power, menu, home, back, and volume). I have searched through all XDA forums and keyworded the net for hours, convinced that there had to be a free or cheep way to unbrick my hard bricked I747. I found leaked instructions that outlined how to bridge a specific (very small) transistor (named R313) inside the phone in order to trigger "SD Card Mode." The SD card was prepared to reinstall boot img and stalk ROM prior to triggering SD Card Mode. However, after opening my phone I found that the phone used to illustrate and show where the R313 transistor was located was designed totally different than my model. There was no way to know where the R313 was. Evidently, the S3 design can differ depending on carrier or maybe time purchased.
So, if it is unlikely for most of us that we will be able to find and bridge the R313 transistor, then there are only two other solutions that I was able to find. TJig, which is about $60, or send phone to Samsung for warranty service (if still under warranty). My phone is still under warranty and I just sent my phone in to Samsung. The question remains, "will Samsung be able to see if a hard bricked phone is customized or has a flash count?" or do they even look. If phone hard bricked, one can boot the phone into download mode with the right equipment. Download mode reveals the flash count. If Samsung checks flash count, then I assume TJig may be my only option. Or maybe Samsung will offer to unbrick my "out of warranty" phone for less than the price of a TJig. Hard to say. I will post my results when I get them.
If you are out of warranty, you may try calling around to service providers. The S3 is still the most popular phone on the planet; there is a good chance that a serve provider somewhere has a TJig and would charge you $20 or so to fix your phone with it.
Please add to this post if you can contribute. Especially if you have gone the warranty route and can report what happened.