I don't ever think there is an easy answer. We live in a rural area by a courtyard development known as hard to sell simply because they are not particularly attractive with only one having a garden.
The "quick" seller took two years and she wanted £225,000 for the house and £125,000 for the small building plot. She sold because she sold both for £250,000.
However, this year after 2 1/2 years on the market her neighbour sold for £225,00 without land! I have to say they had made a lot more effort with the house although some of it (kitchen) was done on the cheap. But it was dressed for the photos, cushions, pictures, lighting and it looked good on rightmove and you would want to view.
I worked for an estate agent years back and when people came into the office I would always suggest an extra property to view. You cannot force someone but I would always say that this one is really nice and not too far away, well worth a view. Your agents need to be pro-active. Have you been into their office (assuming they have one) and seeing how the staff react?
I always remember selling my late mum's house via a small local estate agent. I went in and the staff member was on the phone and completely ignored me for around ten minutes. When I got home she had left a message on my answerphone saying "Sorry I didn't have time to speak to you today..." What? I went in a week later and she acted like she didn't have a clue who I was. Agents are only as good as their staff.
To sell my dm's I repainted it throughout and it did look at lot fresher but it was really hard work. Bought some nice cushions etc from Dunelm and it looked better but I couldn't afford to put in a new kitchen etc. It took three days to sell with the new agent.