My advice is always to never take the first offer. Make a counter-offer that is a little sweeter for you around $5 to $7k higher and see what happens. Be sure to consider though how long your home has been listed. You might not want to play games if your house has been on the market for a while and this is your first offer. Otherwise, go for it!
I believe the first offer is usually the best offer, as well. Especially if it comes in within the first week or two listing. And you don't always counter, especially if the offer is more than fair and you are satisfied with it. It's not always about the $$$, remember. Look at the terms of the offer as well.
You wanted $89,900. Are you happy with $80k selling now as opposed to selling for "who knows what who knows when"?
What did you end up selling for? Let us know!
But it also is possible that the offer (with the counter offer you make, and the counter offer they make back) will be the best. Old Realtor legend says that "the first offer is the best offer", and I have seen that confirmed over and over.
Some improvements, like fixing a garage in disrepair or maintaining the house plumbing, are considered your obligation, not a bonus to add to the selling price.
Generally, this is one of the times you refer to your agent, process comparison information, and formulate a plan. A good counter would be one that was based on information that could be used to support it.
Any insight provided based upon the information you have provided would be "purely guess work."
You deserve much better!