How to purchase off market single family deal?

[Jeremiah Lee]

I've only purchased a home using a mortgage, so I'm very new to this as you can tell.  

Let's say you make an, "all cash offer" which you plan to fund from your HELOC on a single family home and it's accepted by the seller.

-For newbies, would you suggest using a Realtor to write up the contract?

-If I used a realtor to write up the contract, I would assume that I would pay 3% commission to my realtor and there would not be any additional commission paid.  So if I offered $100,000 for the home, I'd actually be paying $103,000 total.

-In this scenario, does the seller often use a realtor or broker? 

-I imagine the majority of this is negotiated between the buyer and seller, however what have you seen as a standard for making cash offers on off market deals?