In a recent double closing deal I did, I lent my money to the company and I only charged a half percent to use my money.

At what percent do y’all run expenses on a four-plex which include maintenance, vacancy, property- management, and cap-ex

I'll add that besides significantly better tax benefits than the S&P, passively investing can offer you: a consistent income stream that isn’t impacted by the ups and downs of the stock market, reduced risk with higher returns (Outperformed the stock market for the past 30 years), you own a real tangible asset (not trading paper for paper) Generates reliable cash dividends of 7 – 10% (paid out monthly in some cases) Once in a lifetime trend creating more renters and driving growth, professional management, Inflation protection, more resilient to market downturns. 

He is considering a commercial loan with an interest rate of over 6 percent.

I get the dogs for the blind, and have a blind cousin who has had several in her lifetime. 

If not, what percent below asking?

Three percent is low, but is that what your employer is going to pay you?

It's probably best to draft up an agreement with all parties, and divide any proceeds according to the percent of money invested like @Nathan G. described. 

If not, what percent below (or above) asking?

Yes Jon I agree with you a hundred percent.