Homes listed for a year without a sale normally indicate at least one thing - the price is too high. If you've got an offer, negotiate, make it work. I do not know the details of your situation, based on your story at facevalue, I'd take it. Your Realtor's job is to bring your an offer. Assuming the your home is being properly marketed, if I were your listing agents I'd have asked (and obtained) price reductions.
I was just coming back to mention that I tell all my sellers to expect the offer to come in low. That is just the market. Negotiate what you can until you are satisfied with the deal.
In this market be thrilled you have an offer.
It's hard to say but if your property has been aggressively marketed for over a year, $16,000 below asking might be about right in your market area. Many communities in Michigan are depreciating in value.
Please review duel agency on the forms you signed. The forms will specify your agents responsibilities and duties to each party.
In today's market more than 95 percent of all offers have to be negotiated. Sorry I cannot elaborate further.