I have had a success rate of over 95% with sole mandates in the last year and today I refuse to work on any other system because the advantages of sole mandates are so clearly apparent.
When only one agent is involved in a sale:
The more one sees estate agents at work, the more one realises that, provided the seller chooses a good operator, sole agencies work best - and the way to check whether the proposed agent is a top performer is simply to ask for proof of recent sales and the telephone numbers of a few previous clients.