Caaron,

This response is just for the occasional person you mentioned who takes offense when you decline their services. When somebody listens to the same song you just listened to, but they hear "cha-ching" while you hear "ba-boom"...

It's hard to hear an opinion we don't like, and easy to disagree with something we can dismiss as easily as personal opinion.

But if you can run whatever these people submit through software like Melodyne that can show a graphical representation of how well each note sits where its supposed to... in terms of both pitch and timing... you might not have to offer your opinion at all. Let the picture do the talking.

https://www.dropbox.com/sh/ey71h8ep047758h/AAC12jNM0Hz9Q8zsh5iDeqNHa?dl=0