You will capture the vernacular used by the speakers (yes, even if it’s not grammatically correct) in the transcript. This is the standard assumption.

Always transcribe vernacular unless you are instructed otherwise.

Speaker says...
I'm gonna go home
I'm gonna go home
I'm going to go home
I'm talkin' 'bout you
I'm talkin' 'bout you
I'm talking about you
I went 'cause you told me
I went 'cause you told me
I went because you told me

When "Non-vernacular" is requested, please do not fix contractions as "don't", "doesn't", "isn't", "aren't" or "I'm". Only focus on more "verbal" contractions such as "d'you", "Imma", "lemme", "hafta", etc.

**When using smart/curly quotes to replace letters or numbers in vernacular, they should always face to the left, as with contractions. When this is at the beginning of a word (’cause, ’em, ’bout, ’kay, ’19), Word will not automatically do this. To get them to face the correct way, hit Control+apostrophe+apostrophe. Alternatively, you can use all straight quotes in the whole file. Don't mix straight (') and smart (’ and ‘) quotes in the same file. This includes double quotes.

Wrong: ‘cause, ‘em.

Correct: ’cause, ’em.

Wrong: [when referring to the 1990s] ‘90s, 90’s, 90s, ‘90’s, ’90’s

Correct: ’90s (or '90s if using straight quotes throughout the file)

Note: "cause" without an apostrophe is a completely different word than