In Michigan, we can only use 5% sellers concessions, anything else needs to be handled outside of closing, any chance that they are using the 8900$ in concessions, and then giving you the 4100$ outside of closing? If not, I would try to figure out why the hell they think they can just charge you and extra 4100$ dollars. Also, I am assuming it is an expensive house, cuz the realtors around here never give money back, so congratulations. 
During the 1st call, the realtor stated that the seller agreed to pay 'up to $13,000 of the closing costs' and was trying to differentiate between the closing costs and the total cash to close (which includes the down payment, of course).
The home price is only slightly above the median for our area (Sacramento suburbs), but I guess that is still a bit higher than the national median.
The realtor has been nothing but shady. When I decided to go for this home, she said that the seller was offering her an incentive if I would agree to close by the end of October (but then they actually wanted it a week earlier...a 20-day escrow).
Keep in mind that I found this home on my own and the wife actually monitored the price drops over the past 9 months. The realtor is basically along for the ride. She said to us, "the incentive is a couple thousand dollars, so I'll split it with you". She already knew that I verify
everything, which I started doing after catching her in some lies before, but she tried to act pissed off when I found out that the bonus was actually FOUR thousand dollars. I was at home when I found out and called her immediately to find out what kind of game she was running. She smarted off a couple of times and although I wanted the full four thousand, I agreed to a compromise amount of $2000.
Even taking back $2000, though, the brokerage is still WAY overpaid on this deal. She complained that I was trying to 'take her entire commission', and I told her flat out that her company's services were worth nowhere near the $17,000 they stood to make on the deal if I hadn't demanded some back. She said that the $2000 would come out of her half of the total commission and I told her that was between her and her firm.
I won't ever use an agent again (unless I'm out of the area and absolutely cannot get a deal done on my own), but trust me when I say that I've got a full list of tips and warnings that
every first-time or inexperienced buyer should know before getting into a deal with a realtor.