As far as listing commissions go, it varies, but I usually charge 6% of the sale price. I split a portion of this commission with the buyer's agent (cooperating broker).
Please remember that there are other cost to consider when selling a property in Chicago.
1. Prorated Cook County Property Taxes, which are usually 1 year arrears. If your mortgage company is holding an escrow, some of this money should be in the escrow.
2. City of Chicago Transfer Taxes, and State of IL transfer taxes.
3. Water bill Cert.
4. Attorney, Title, Survey, Termites, etc...
I provide an estimate for my clients when we discuss a listing. I also recommend they discuss their sale with an attorney to generate a preliminary HUD-1 if they are concerned there may not be enough funds.
Many sales these days are Short. In other words, the lender must reduce the payoff to the homeowner to facilitate the sale. In cases where the underlying mortgage is more than the home will sell for in todays market, a short sale is the only option.
When the underlying mortgage is close to property value, usually then is can get confusing for the seller. Many times in these cases you will not know if the sale is short or not until the buyer makes an offer. If you don't have funds to cover the underlying mortgages and closing cost, usually the bank will agree to a reduced payoff. This can be a frustrating process, but it happens everyday.
Best of Luck.