You should get at least three valuations from different agents, in order to get a good idea of the value. You don't have to accept the valuation which the agents give you. If you believe that the house is undervalued, then you should point out why you think it is undervalued. The agent should market your house, for a price which you agree with.
Agents and potential buyers should be able to see through cosmetic problems. Value is more dictated by the the things that can't be changed, ie the direction of the garden, the size of the plot, the size of the house (which can be changed by an extension, provided by the plot)
I looked at a house a couple of weeks ago. The house was well over priced for what it currently was, but it had the potential to build an extension. The vendors had factored in the potential extension, even though they hadn't built it!!
I thought that you could buy a house which was perfect on the inside, but have come to the conclusion that it doesn't exist. Every house requires work. Even if it is perfect now, by the time the current owners takes down pictures and moves furniture, then the walls need to be re-painted.
In conclusion, agents and buyers should be able to see past cosmetic issues, provided the house is structurally sound, you should be OK.