Yup- for $850,000 6 points is par. Granted- you can say the buyer is paying the fee- but you know there is no free lunch. If the buyer is truly paying the fee, the buyer will pay less accordingly.
Anyhow, you will be able to get paperwork from them about the commission %. However, there is always a chance that they could be in 'cahoots' and inflate the commission with a kickback from the broker back to the buyer. But seriously, just do what makes sense from your end and who cares how they run their end? If you believe fair rent is X, pay X. Don't get sucked into paying rent based on price + closing costs + commissions. Simply ask the seller for the end number, and if its good pay it. If not, counter. The commission business should be irrelevant from your perspective.
Good to hear that things are progressing favorably for you. Isn't money great?