Free chord charts and tabs online are often incorrect
I get a lot of requests from my guitar students to teach them particular songs that they like and I'm happy to oblige. A lot of my students download chord charts and tabs from the Internet themselves only to get frustrated because it's difficult for a beginner to learn new songs just from some chord symbols or tabs without rhythms -- especially if the transcription is wrong!
And boy there are a great many tabs and chord charts online that are wrong!
Keep in mind that when you Google "Jason Mraz tabs" you will get many results but none of them will be written by the artist himself. Many of them could have been transcribed by people with very little experience in music and even less experience transcribing songs.
I've seen some tabs online that are preceded with words like "Please be kind this is the first tab chart I've ever created," which I find honest and kind. At least you will know to be cautious because the chart may have errors.
I have also read comments from many people on the Internet who think they can learn how to play guitar just by downloading tabs, chord charts, and "free lessons" from the net. Certainly there is some amazing content on the Internet today. But there is just as much garbage and when you're a student how will you know what is good advice and what is bad?
"She Says" the chords are wrong
Here's an example of what can happen: One person has uploaded an incorrect chord chart for a Howie Day song and afterwards people have posted videos of themselves on YouTube playing the song incorrectly, without knowing of their errors.
One of my students is working on Howie Day's "She Says." I transcribed the chords in the first verse for him during our lesson earlier this week. Being a diligent student he has already practiced the chords I gave to him and now he wants to learn the rest of the song.
He went onto YouTube to find videos of people playing the song, to try to figure it out on his own. He e-mailed me a link to this fellow playing the song.
I watched the video and heard right away that the guy's not playing the song correctly. He's got the rhythm right but he's missing one chord in the verse (he's playing Cadd9 – C – Cmaj7 correctly, but he plays it over and over, missing out the really sweet Am chord).
I did a quick Google search and found free chord charts online that are wrong – many of the chord charts online also leave out the Am chord in the verse.
So now, just because one person uploaded an incorrect chart to the Internet, many people are playing the song incorrectly. Maybe it doesn't matter too much. It still sounds nice. But that Am chord adds a lot and the song is somewhat lacking without it.
It's not that surprising that the Am chord was missed. If you don't have a lot of experience transcribing songs, your ear might not notice the change from Cmaj to Am because the two chords are very similar. Am is the "relative minor" of Cmaj and they share some of the notes (C and E).
So the song still works if you skip out the Am and continue playing Cmaj, but the verse sounds less varied (and less interesting) when it's stuck on the Cmaj harmony.
I recommend to any beginner guitar player, who wants to learn particular songs, to find a good guitar teacher who can teach you how to play the songs you want to learn and how to play them correctly. And of course a good guitar teacher can also help you learn proper technique, understand harmony, read music, transcribe songs, write your own songs, etc. etc.