I don' t think you need to use an independent website, you can search for cancellations on the DVLA website. DS did this after a series of lessons, booked a test about 10 days away and then drove as much as possible beforehand. He passed. You just put in your licence/theory pass details and search for a cancellation.
I passed my test this way - through just checking the website. Don't pay extra for the checker.
My instructor was also really good and told me to do it this way. She asked me for my provisional license number and details and she would check it for me hourly. Trick is to always have the website open on your phone etc so you can keep refreshing.
I found this thread while searching for people who have had as negative an experience as me regarding the testfinder.co.uk service. I just wanted to warn others of this scam website!
I paid the £18 for them to find me an earlier test date as I wanted to do it before my holiday. They didn't find me an earlier date, which is not my complaint as I understand these things happen, but upon trying to contact them to obtain a refund I have found it impossible to get a response from them. After many emails I started contacting them on Facebook, they promptly deleted all my comments and subsequently blocked me. So somebody monitors their page but refuses to answer to my messages.
It's only £18 but with over 800,000 driving tests done in the UK each year and an average 12 week waiting time, imagine how many other people they have ripped off and then deleted their comments?
Please do yourself a favour and find a different test finding company or search the dvla website yourself.