Took us 6 years to sell our first house. On lots of internet property sites, one agent who tried for about 6 months then we heard no more, though it was on their books all that time, several others, including Leggatts who all lost interest once they'd had it about 6 months, and then I gave it to a Rotary colleague, also an estate agent (he wasn't in the business when we started), who was also good at marketing, and wanted to sell it and not only because we are friends.
Can't remember just how long he had it for, less than a year, I think, but we had more viewings via him, and yes, he sold it.
So find someone who not only can do the job but wants to sell, it, and proves it too (in other words, they get viewers, and they keep in contact too.
ex W1, via 47 and 11 and now [just] in 34, equidistant from Carcassonne, Narbonne and Béziers, where I hope we'll finally stay!!