I don't think the fact that it's been on the market for so long necessarily means there is anything wrong with it.
My in-laws have been trying to sell their house in Dumfries for about three years. It is lovely, beautifully maintained, no structural problems etc but despite lowering the price to below what they bought it for (getting on for a decade ago) they have had no offers, I think because it is valued at £300k+ which for Dumfries is the top of the market.
I think the economy around Dumfries is just very depressed (the centre of town has declined noticeably) and there aren't buyers around for the upper end of the market.