There is no set commission rate, legally there cannot be one.
In the real world, both list price and commission are marketing tools. If your goal is to sell your home for the best price, meaning net profit to you, then I would focus your efforts on maximizing that number.
You do no sell homes for a living, so you'll have to ask professionals that do.
Here are some facts that will help you ask the right questions:
Homes that sell in the first 30 days sell closest to asking price. In any given market that means that about 20-30% listings sell within 30 days, the rest (70-80%) sell in two, three, four, five months.
In my MLS, homes that sell within 30 days are selling at 99.9% of asking price. at over 120 days they are selling for 93% of asking price. That is a 6% difference.
New listings are expected to have 10-12 showings or one offer in the first two weeks, otherwise we lower the price, usually around 5%. No showings...price is too high. Showings and no offers, price is too high.
How does this relate to commission? You want to sell for the most money. If 70-80% of listings are overpriced, what are the chances that the Realtor you like...offers you the highest price and lowest commission..is right?
Truthfully you need a Realtor that will tell you the truth up front. My newest listing has six offers, most above asking. It's been on the market for five days. My next listing had a full price offer in the first week on the market, will sell at full asking price.
The fact is that if a Realtor's ONLY tool is to offer you a discounted commission, then I would probe deeper. You are paying a professional to:
1. Analyze your home and advise you what you need to do to get top dollar.
2. Figure out what features in your home will attract the most buyers and market those features.
3. Price your home so the other Realtors, who 90% of the time represent the buyer, will say "wow, this is a great deal, let's go and look at this property" so you can get multiple offers
4. Be an effective negotiator, counter back and forth, start a bidding war, and get the most for your home.