What 1st impression does your property make when a buyer approaches and / or enters? Does he see nice landscaping, a mowed lawn, clean entrance door? Or did your kids not pick up the toys last night and the dog tried to enter, leaving marks on the door?
The very first impression your home makes is the same as a person smiling at you for the first time. If she has a front tooth missing and has some spinach between the others you are disgusted, right? Same with an unkempt home. If your property lacks grooming, chances are buyers are discounting it before they even have set foot in the door.
So let's assume they got over it and enter. The very first impression your home will make inside, subconsciously mostly, is it's smell. You do not notice anymore that the dog that left its paw mark on the front door also makes the carpet reek. Your nose has gotten used to it but for your buyer it's the first time. That and maybe the unaired bedrooms? Discount. Kitchen was only halfheartedly cleaned? Discount. Bathroom sinks have hair in them? Discount.
You might think this is foolish, after all, your home has great features, granite counters, wood floors etc etc. But a buyer picks up on maintenance and if your gorgeous home is grimy it will cost you.
My advice is to get a pro cleaner to go over every nook and cranny, shampoo the carpets, wash the dog and be as neat as you can. To groom your property is inexpensive but it will achieve a disproportionally higher price than one that is unkempt.