What @Susanap said.
I successfully sold through PB within weeks, and so did three other people I know. All went smoothly and all the houses went for more than high street agents suggested. A real benefit is viewing times are usually flexible (online diary the viewer can access) with weekend and early evening viewings available if you're happy to do your own viewings.
Once an offer is accepted it's vital to swap contact details so you can communicate directly with buyer / seller which really helps to keep a chain together. Have your solicitor's details to hand too, so you both know who is doing the conveyancing.
High street agents like to rubbish PB and other online agents, but our experiences have all been positive.
High street agents like to keep buyer and seller apart which can make things very difficult, and seriously threatened the chain in our case. Only once I tracked down the buyer (he'd told me where he worked) and contacted him directly did it start to go smoothly - the agent had been trying to fleece either party for add-on electrical and other upgrades (which they take a cut from the referral) which we and the seller knew weren't necessary, and they certainly hadn't asked for.
With PB you can do your own photos and write your own property description, often producing a more professional ad than a high street agent would do - if have an eye for presentation and a decent phone, and can write reasonably well, it's a much better system all round.
You just have to pay around £400 for the Rightmove listing, which is basically the shop window. The rest is up to you.
Long time mumsnetter. I do not work for Purplebricks!