You will be in a far better position in the negotiation process if the improvement is done PRIOR to listing your home.
It may be updating old appliances, removing tired carpet, refinishing wood floors, installing a new heating system, replacing the roof, relining a chimney, whatever it is that is falling apart and/or drawing its last breath.
If you make improvements before listing, you have more control.
You have control, more specifically, over the cost.
Listing a home with new appliances, for example, will cost you less than the allowance and/or price reduction that buyers will want in order to choose their new appliances. Buyers never imagine buying the package of new appliances on sale at Lowe’s. They think of the cost of the Wolf stove they always dreamed of and the Subzero refrigerator. They allocate a price tag to new appliances that is easily double or triple what you will spend before listing.
Not only can you shop for improvements to your home before you list and decide the quality of the improvements you are going to put into the property, but you can also negotiate a better price with the contractors if you schedule your improvements during their down time.
Negotiations between sellers and buyers can be stressful enough without the added stress of having a home inspector announce a new roof or new heating system is needed.
If you choose NOT to make the improvements prior to listing, you risk giving up control and being in a position where you are making responding to the buyer’s anxiety and expectations rather than making a decision from a position of strength.