It had been fixed twice and the last time the roofer told me that a new roof was needed because the roof in that area has too many holes already.

Can anyone recommend a roofer for a 3-family in Hartford?

I would call a roofer first . 

The roofers I have used always try to discourage me from doing it, but if your decking is all sound and the existing shingles are still laying pretty flat is there really any downside to it? 

If you are in need of a roofer, Call HE Roberts (They are out of Milton).

The seller / realtor was supposed to send a licensed roofer out. 

@HAILEY ERSKINE Good for you, get the ducks in the row, start collecting 1) realtor, 2) real estate attorney, 3) cheap title search, 4) CPA, 5) Contractors (handymen, electricians, plumbers, roofers), 6) Insurance. 

If the roofer needs to replace portions of the roof sheathing you have a price upfront that can be used to calculate the Change Order for replacing the sheathing.I think in the past I've been quoted around $35 to $50 per sheet (labor & material).

Can anyone recommend a good roofer in Duval county?

He is a bit higher than most investors like to spend (high side of mid-priced roofers) but I would highly recommend him.