Looking for someone with no musical background

Or no strings background, I'm not too picky.
I'm working on a scene and I need to confirm that it's understandable from an outside perspective, you see my baby Damien plays violin, I play viola, for the matter I'm covering there really isn't a big difference. I need to make sure that my explanation of the issues with the violin are understandable to people who aren't familiar with them. So without further ado, here's my little snippet I just need to know if the way this is explained makes sense:

He takes a violin from a shelf and brushes away dust, “I must say a song isn't an offer I've gotten before. I'm curious to know it's worth.”
It may be the most pathetic instrument I've ever seen, varnish dull and scratched, bow almost devoid of hairs, strings starting to rust, one gone completely. I take it gently, tune the three strings and pray they won't snap. I tighten the bow as best I dare, though it crackles a complaint no bow in good condition would.
West steps back as I bring the violin to my shoulder, “If I um if I do this you ah you swear you’ll tell us everything you know about the um the cambion killings?”
Samael sits on his counter and crosses his heart, “Death is fair child, if nothing else death is fair.”
I can’t say I agree, but I have his word and that is the best I can hope for. I put the sad little bow to the string and start to play.
The violin is an instrument that thrives on technique, a little vibrato turns a boring piece into something beautiful, some shifting can make up for a missing string, a finger laid a millimeter too high or too low can completely change a note. Technique I can manage, but the string isn’t the only thing missing on this violin; there’s no shoulder rest. Without the shoulder rest I have to work harder to keep the violin on the right place with my shoulder and chin, which puts me in an awkward position where I can’t easily move my hand down the neck of the instrument to change positions, and my wrist ends up bent against the instrument without any space for the extra flourish that creates the richer sound of a vibrato note. Between the missing shoulder rest and having only three of the four strings I don’t have the full range of the instrument to work with, which essentially makes me musically crippled.

I actually do play viola and piano, but that's not what I'm commenting on. The dialogue needs a little bit of grammatical editing in some places. Here, I'll show you what I mean-
“If I um if I do this you ah you swear you’ll tell us everything you know about the um the cambion killings?” I believe you need to have some sort of divider between the 'um's and the rest of the sentence.
For example:
"Um, if I do this… do you, ah, swear you'll tell us everything you know about the, um, the cambrion killings?"
As for the next dialogue piece, Samael's line, “Death is fair child, if nothing else death is fair…", I think you'd need either a comma or period in there.
For example:
"Death is fair, child. If nothing else is fair, death always is." or "Death is fair, child. If nothing else, death is fair."

Also, you have one or two run on sentences in there that should probably be tweaked. There's also some basic edits for grammar that would really take this to the next level. I'll show you what I mean-

1. There needs to be a period after the word dust in the first line. Ex: "… and brushes away the dust. 'I must say, a song…' "
2. There also needs to be a period instead of a comma before the 'death is fair' line. Ex: "Samael sits on his counter and crosses his heart. 'Death is fair…' "
3. "The violin is an instrument that thrives on technique, a little vibrato turns a boring piece into something beautiful, some shifting can make up for a missing string, a finger laid a millimeter too high or too low can completely change a note." If I were you, I'd separate this sentence to make it flow better. Ex: "The violin is an instrument that thrives on technique. A little vibrato turns a boring piece into something beautiful, some shifting can make up for a missing string, and a finger set a millimeter too high or low can completely change a note."
4. "…there’s no shoulder rest. Without the shoulder rest…" You used the word 'shoulder rest twice. I might suggest just changing the second one to 'rest' because people will already know what you mean. This is being picky, but I thought it might be good to know.

The only thing I would suggest for your original question is to maybe edit the last paragraph a little. A lot of people might not know what vibrato is, so you might want to think of something to casually clarify that a bit. Other than that you're probably fine.

Oh dear I hadn't noticed that! Thank you for letting me know, I'm still in the first round of editing and since my grammar check really only tells me if a word is misspelled so it's easy to miss things.

And thank you for the input on the vibrato I think I actually know how to clarify that.

That's helpful! I may just have to go back to word with that as an option.

So I have no musical experience really(unless you count playing the ukulele when I was five and listening to my friend talk about violin some)
It was very detailed and I thought you did really well explaining and it was nice. Although I didn't fully understand everything I got the general idea of what was going on

Thank you so much! I'm glad it comes across well enough that the general idea is communicated even if not everything was spot on understandable.

You definitely did that! I really liked it and felt like I might have learned a bit as well, lol.

Thank you for the input! I'm glad it works!