DO NOT BUY FAKE CERTIFICATES.
One of my students recently bought one of these before booking a lesson with me and she has now unfortunately lost more than $3,000.
These scammers usually use Western Union so there is no security for your transaction. There is no way for you to reclaim the money.
But most importantly: it does not work. The easiest way to pass the exam is to study and get the right band score. Immigration offices have grown very strict over the past few years and they are very observant of this type of scam. It is not recommended that any student tries to buy a certificate.