Giving it away for free to deadbeats is what got him inundated with crappy messages. If you make a product and sell it, then the people you'll end up communicating with are more professional users. If you give it away for free then go check out reddit.com/r/choosingbeggars to see what kind of idiots you'll attract.
We sold 10's of thousands of training videos, over the 15 or so years we had something like 80% of emails just to say thanks for making the video, 20% asking for help on a project they were making from the video and I think to the best of my knowledge we had like 2 complaints ever; 1 DVD got lost in the mail and the other was someone complaining his internet was too slow to download the video without timing out.
Flip to our youtube channel for free stuff and we have message after message...
Why haven't you updated this video to the latest version
I know a better way to do the effect than you
I can do this better in blender
You breath too heavy
I dont like the sound your lips make by the microphone
You speak too slowly
You go too fast
....
Give something away for £0 and the value of the feedback you get will also be £0
Heck, go sell it to insydium and cash out. Never have to deal with another customer ever again