We've have the same problem, from the outset I knew it was going to be challenging to sell a six bed house, in not the best of areas, I can see the new power from waste power station from the front garden! However after 18 months we accepted an offer at £15k below the price we wanted.
So what did we do to get a sale?
I selected the estate agent carefully, I went with a new agency opening up in town, the manager was keen to get the business up and running and worked hard to market the property, we changed the photos three times and relisted it on Rightmove twice, so that it would get posted to those buyers who'd set up "new to the market" alerts.
I negotiated hard for a fixed fee, which equates to 0.75%.
we continued to paint and decorate rooms and the exterior, not everyone is looking for a project, people want to be able to walk into a place and get on with life.
we preened the gardens, there is nothing worse than a weedy overgrown garden.
finally, I'm getting out of 'buy to let' it's just a pita. If you need to rent, look at your likely yield and consider how you would deal with maintenance and breakdowns. Then there's void periods, dealing with tenants that cause problems (I've had weed being grown in the back bedroom, a cat lady, when the t&cs says no animals, non-payers, moonlight flitters and someone who set fire to the house during an argument with his partner).