BT Broadband's Accelerator - the service the broadband provider offers to maximise customers broadband speeds - has come under criticism from some quarters.
There have been suggestions the £90 fee for an engineer, which is subject to additional costs should a workman have to stay for longer than an hour to make the necessary changes to customers' broadband set-ups.
However, the company is offering a money-back guarantee for instances when a customer cannot be given a speed increase of over 0.5 Mb.
BT told customers in a statement: "In order for us to maximise your broadband speed we will test your existing speed, and see if we can improve your speed by at least 0.5Mb. At this point, if we cannot help you will get your money back.
"We will then book your engineer visit to improve your broadband speed by optimising your home computer, internal wiring and home networks."
The Accelerator initiative comes after the launch of BT's Interstitial Plates - devices designed to aid broadband connection.