amateurdiyer

Hi guys, We have recently moved house and had all the windows and doors replaced. we used a local company in Chesterfield to supply and fit the uPVC windows. They look absolutely great but we have now decided to add a door knocker to the front door. The company wants to charge us £100+VAT for fitting it. Is this reasonable? Will it void any warranties? Here is the door knocker we have bought: https://door-knockers.co.uk/product/large-brass-arts-and-crafts-doctors-door-knocker/ Thanks in advance for any help.

Hey everyone, Myself and my wife are new to the DIY Scene and have just bought our first house to flip. Sorry in advance if we post some obvious questions!?